"Happy sesquicentennial" is a mouthful, so let's just wish the Smithsonian Institution a happy birthday. It was 150 years ago -- Aug. 10, 1846, to be exact -- that President James K. Polk signed into law something called the Smithsonian Act of Organization. The rest is history. Not to mention technology, zoology, art and everything else you'll find at the Smithsonian.

Hardened Washingtonians often take the Smithsonian for granted. We tell visiting relatives that they should be sure to "go to the Smithsonian," as if it were one place, one building, one museum.

We've been there ourselves, but, well, it's been a while. Nowhere to park, we say. Full of tourists.

Some of us even call it the Smithsonian Institute. (Ouch.)

And yet there's possibly nothing inside or outside the Beltway that's more accessible to us all. The Smithsonian has something for everyone. Fossils and spaceships. Paintings and weapons. IMAX movies and miniature portraits. Pandas and peccaries. Ball gowns and ball-peen hammers. If you can't find something to pique your interest, engage your intellect or caress your eyeballs at one of the Smithsonian's museums then you don't have a pulse.

And what a bargain! Go to Paris and you'll pay to see the Mona Lisa at the Louvre. Go to New York and they'll dun you at the MoMA. Heck, go to Baltimore and you'll find yourself pulling out your wallet. We get it all for free, just for living where we live.

There's a lot to the Smithsonian -- research projects, magazines, festivals -- but it's the Washington museums that are the core of this institution that's devoted, in the wonderfully understated yet open-ended words of its benefactor, to "the increase and diffusion of knowledge."

On the following pages we at Weekend diffuse a little knowledge of our own. Our anniversary poster has everything you need to know about the Smithsonian, from what you'll find at each museum to tips on getting the most out of your visit.

This weekend is a good time to visit, since the Smithsonian is throwing itself a sesquicentennial birthday bash on the Mall. (We've provided details on that, too.)

And we're all invited. Celebrate With The Smithsonian

The Smithsonian Institution celebrates its 150th anniversary this weekend with a wide range of special activities, and they're all free. In addition to these scheduled performances at sites across the Mall and at the Anacostia Museum, more than two dozen pavilions on the Mall will house exhibits, talks and demonstrations. Most of the individual museums are also holding their own open house programs, with special tours. The "Sweet Smithsonian" pavilion will display 19 (non-edible) birthday cakes by chefs across the country, including a six-foot replica of the Castle. Sixteen local restaurants will sell their specialties at booths near Fourth, Seventh and 14th streets from 11 to 9:30.

A highlight of the weekend is the gala outdoor concert at the Castle Saturday at 6:30, with Aretha Franklin, Trisha Yearwood, Buffy Sainte-Marie, Mickey Hart and the Smithsonian Jazz Masterworks Orchestra. The concert will be followed by fireworks.

A free brochure with schedules and a map will be available on the Mall. The National Air and Space Museum, the National Museum of American History and the National Museum of Natural History will be open from 10 to 9:30 Saturday and Sunday; the other Mall museums will be open from 10 to 6; and the pavilions will be open from noon to 6.

Free shuttle buses will run from the National Museum of Natural History's Constitution Avenue entrance and from Fourth Street near the National Air and Space Museum to the Anacostia Museum, National Museum of American Art, National Portrait Gallery, National Postal Museum, National Zoo and Renwick Gallery.

For general information, call 202/357-2700 (TDD: 202/357-1729). Outdoors CASTLE STAGE -- At the Smithsonian Castle, 1000 Jefferson Dr. SW. Saturday: Opening ceremony with the U.S. Marine Corps Band and remarks by dignitaries, at 10:30; KanKouran West African Dance Company, 1; Cambodian American Heritage Dancers, 2; Zuttermeister Hula Halau with the Ho'opi'i Brothers, 3. Concert at 6:30 by Aretha Franklin, Trisha Yearwood, Buffy Sainte-Marie, Mickey Hart and the Smithsonian Jazz Masterworks Orchestra, followed by fireworks. Sunday: The Smithsonian Chamber Orchestra, noon; Footworks Dancers, 1; Tap America Project, 2; Asian American Arts Center Drummers, 3; Nilimma Devi Dance Theater, 4. Procession at 5:45 by the American Indian Dance Theater and the Lakota Sioux Dance Theater. Concert at 6:30 by Steve Riley & the Mamou Playboys and Celia Cruz & Jose Alberto El Canario & His Orchestra. MONUMENT STAGE -- On the Mall at 14th Street. Saturday: Celtic Thunder, at noon; the Birmingham Sunlights, 1; Image Band, 2; Shashmaqam, 3; Bobby Parker & the Blues Night Band, 4; Klezmer Plus, 5. Sunday: Soh Daiko Japanese Drummers, noon; Six Nations Women Singers, 1; Mariachi Los Amigos, 2; the Birmingham Sunlights, 3; Richard Smallwood & Vision, 4; the Dixie Hummingbirds, 5. CAPITOL STAGE -- On the Mall at Third Street. Saturday: Soh Daiko Japanese Drummers, noon; Johnny Gimble, 1; the Freedom Singers, 2; Ruth Brown, 3; Little Anthony & the Imperials, 4; the Tuxedo Brass Band, 5. Sunday: The Midnight Movers, noon; Boozoo Chavis, 1; the Capitol Steps, 2; the Pan Masters Steel Orchestra, 3; Steve Riley & the Mamou Playboys, 4; the Terri Lyne Carrington Group with Sheila E. and Everette Harp, 5. "IT'S PUBLIC KNOWLEDGE" -- Actor E.G. Marshall hosts discussions and debates in a pavilion on the Mall in front of the National Air and Space Museum. Saturday: "Loudmouths: Tune In? or Turn Off!," with Paul Duke, Chuck Conconi, Sarah McClendon and Brad Keena, 1; "The Battle of the Sexes," with Maureen Bunyan, Deborah Tannen and Jim Bohannon, 3; "Whose Culture Is It Anyway?," with Jim Weaver, Larry L. King, Kitty Carlisle Hart and Joe Barber, 5. Sunday: "The War of Words," with Robert Aubry Davis, Paul Dickson and John Morse, 1; "Acting Your Age?," with Mary Catherine Bateson, Rue McClanahan and Elizabeth P. Campbell, 3; "To Web or Not to Web " with Adam Clayton Powell III, Richard Leiby and Richard Thorpe, 5. CENTER FOR FOLKLIFE PROGRAMS "KIDS' TENT" -- Activities for children in a pavilion on the Mall in front of the Arts and Industries Building. Saturday: Percussionist Barnett Williams, noon; Panamanian Youth Cultural Association, 1; Storyteller Len Cabral, 2; Hellenic-American Academy, 3; Singer Ella Jenkins, 4; Baileys' Kids, 5. Sunday: Center for Ethiopian Arts & Culture, noon; Washington School of Chinese Language & Culture, 1; Storyteller Bill Harley, 2; Baileys' Kids, 3; Singer Ella Jenkins, 4; Hellenic-American Academy, 5. Indoors HALL OF MUSICAL INSTRUMENTS -- In the National Museum of American History, 14th and Constitution NW. Saturday: Smithsonian Chamber Players, 1; Ella Jenkins, 2; Beverly Cosham, 3; Ollantay, 4. Sunday: Buck Ramsey, 1; Ella Jenkins, 2; Smithsonian Chamber Players, 3; Robert White, 4. CARMICHAEL AUDITORIUM -- In the National Museum of American History, 14th and Constitution NW. Saturday: Ruth Brown, 1; Bobby Parker, 2; Mariachi Los Amigos, 3; Celtic Thunder, 4. Sunday: The Dixie Hummingbirds, 1; Klezmer Plus, 2; Footworks Dancers, 3; Boozoo Chavis, 4. BAIRD AUDITORIUM -- In the National Museum of Natural History, 10th and Constitution NW. Saturday: Little Anthony & the Imperials, 1; Trisha Yearwood, 2; Boozoo Chavis, 3; KanKouran West African Dance Company, 4. Sunday: Bahamian Junkanoo Rush-Out, 1; Celia Cruz, 2; the Terri Lyne Carrington Group with Sheila E. & Everette Harp, 3; Tap America Project, 4. MEYER AUDITORIUM -- In the Freer Gallery of Art, at 12th Street and Jefferson Drive SW. Saturday: Ho'opi'i Brothers Hawaiian Dancers, 1; Nilimma Devi Dance Theater, 2; Buffy Sainte-Marie, 3; Cambodian American Heritage Dancers, 4. Sunday: Shashmaqam, 1; Djimo Kouyate & Family, 3; Zuttermeister Hula Halau with the Ho'opi'i Brothers, 4. RING AUDITORIUM -- In the Hirshhorn Museum, Seventh and Independence SW. Saturday: Buck Ramsey, 1; Six Nations Women Singers, 2; the Image Band, 4. Sunday: The Pan Masters Steel Orchestra, 1; Johnny Gimble, 2; the Freedom Singers, 3; the Capitol Steps, 4. Away From the Mall ANACOSTIA MUSEUM -- At 1901 Fort Pl. SE. Free shuttle buses will run between the museum, the Mall and the Anacostia Metro station. In addition to the performers on the main stage, there will be storytellers, family history workshops, crafts demonstrations and food vendors. Saturday: Mike Baytop, noon; Groove Phi Groove step dancers, 12:30; Haitian music by Harry Azemer, 1; Jackie & Associates Trinidadian carnival dancers, 1:30; Crystal Fleary, 2; D.C.'s Finest, 3; Mary Jefferson, 3:45; Imani & First Prayer, 5. Sunday: Crystal Fleary, 12:30; Archie Edwards, 2; In2Lect, 3; Steven Herring, 3:30; Fabian Barnes Dance Ensemble, 4:15; Salvation Music Ministry, 5:15. CAPTION: SMITHSONIAN; 150: AN ANNIVERSARY GUIDE TO THE NATION'S ATTIC THE PAST: The Man Who Made It Possible

James Smithson was a rambling, gambling English scientist who never saw his father and never was admitted to his ancestral castle. Born in 1765 of an English lord's summer dalliance with a widow of Bath, Smithson was in his thirties before he was allowed to use his father's name. Although his mother was royal, and very rich, Smithson's illegitimate birth denied him any social standing; he couldn't even go into the army or civil service. Intelligent, energetic and adventurous, he was also bitter. "On my father's side I am a Northumberland, on my mother's I am related to kings, but this avails me not," he once wrote. "My name shall live in the memory of man when the titles of the Northumberlands and the Percys are extinct and forgotten."

For most of Smithson's life that assertion seemed unlikely. Although he was elected to the Royal Society when quite young, his scientific accomplishments were modest.

Smithson died childless and relatively unknown in Italy in 1829 and was buried there. But by one last stroke -- his signature on his will -- Smithson achieved his ambition of immortal fame. By leaving his immense fortune of 100,000 pounds ($508,318.46) to the young United States, to found in Washington, under the name of the Smithsonian Institution, "an Establishment for the increase & diffusion of knowledge," he forever welded his name to what would become one of the greatest intellectual organizations in the world. Its headquarters became his final resting place when his sarcophagus was moved to the Castle in 1904; true to its mission, the institution's scientists examined Smithson's remains and determined that he had an extra vertebra -- plenty of backbone, in other words. THE FUTURE: Visiting the Smithsonian From Home

Virtually everyone is talking about how universal computer networking is the wave of the future, but Smithsonian Secretary I. Michael Heyman is doing something about it. The day he took office Heyman ordered the institution online "with highest priority." He intends, he says emphatically, to oversee nothing less than "the electronic transformation of the Smithsonian." The "Electronic Smithsonian" page leads off with James Smithson's dictum that "Knowledge should not be viewed as existing in isolated part, but as a whole. Every portion throws light on all the others."

The institution's home page (http://www.si.edu/) debuted in May 1995 and immediately began registering some 4 million "hits," or visits, per month. Every few weeks another museum, branch or office of the Smithsonian inaugurates its own home page. Virtual visitors from anywhere in the world can cruise for schedules and snippets of exhibitions and other activities, find out what's gnu at the zoo, visit the Smithsonian's New York City venues, or plug into the institution's libraries and worldwide research centers. One can even tour the Smithsonian of a century ago. It's possible to spend hours or even days exploring the intricately interconnected subsites.

Cruising the electronic Smithsonian can be a bumpy ride -- the information available varies from extensive to superficial; few complete virtual exhibits are offered, and they're dropped when the actual exhibit closes, as though cyber time were dependent on real time -- but it gets more interesting almost every day. SMITHSONIAN INFORMATION

* Admission: Free to all Smithsonian museums and the National Zoo.

* Hours: Most of the museums are open every day from 10 to 5:30. (Hours at some museums are extended in the spring and summer.) The National Zoo grounds are open daily 8 to 8 from April 15 to Oct. 15, 8 to 6 from Oct. 16 to April 14; most animal buildings are open 9 to 4:30. The Anacostia Museum's hours are 10 to 5 daily. All of the Smithsonian facilities are closed Dec. 25.

* For information: Call 202/357-2700 for information on all Smithsonian museums. TDD: 202/357-1729. Daily recorded information: 202/357-2020. Daily Spanish recorded information: 202/633-9126. THE SMITHSONIAN CASTLE is the answer to the tourist's age-old question: Where's the Smithsonian? The institution's original building -- designed by James Renwick and built in 1855 -- now houses the Smithsonian Information Center. Videos, interactive computers and knowledgeable docents offer information on the Smithsonian's many venues as well as other Washington tourist attractions.

TIP: The Smithsonian Associates Member's Dining Room in the Castle has such 19th-century ambiance it's almost worth the price of annual membership ($45 individual, $55 couple, $58 family) by itself. THE NATIONAL PORTRAIT GALLERY builds a picture of America by gathering pictures of Americans. Often they aren't pretty pictures; the gallery takes the good, the bad and the ugly along with the famous, the powerful and the beautiful. All our notables are noted, of course, especially entertainers and most especially our presidents, but the gallery also takes notice of nonentities. Anonymous portraits are often acquired because they exemplify the extremes of the American character and experience; sometimes they're acquired because they exemplify what seems ordinary today but may be seen as extraordinary tomorrow. The collection includes the works of great painters, sculptors, caricaturists and photographers along with pictures produced by people who had no idea they were making history. Yet for all its seeming randomness the gallery's collection has a powerful coherence arising from the fact that the human face and figure are the most consistently arresting of all images.

TIP: Don't miss the Meserve Collection of Lincolniana on the top floor; it will reintroduce you to a great man you thought you knew. THE NATIONAL AIR AND SPACE MUSEUM has the Wright stuff: Orville and Wilbur's original Flyer, Lucky Lindy's Atlantic-hopping Spirit of St. Louis, Chuck Yeager's sound-barrier-shattering Glamorous Glennis, space vehicles, chunks of the moon, even a Soviet nuclear missile that once was aimed at us. And of course the controversial atomic bomber Enola Gay. For the most part Air and Space is a hardware store that celebrates the bright stuff: big shiny machines and the men and women who've flown them first, fastest and farthest. The hardware hanging overhead and the interactive exhibits at hand educate and illuminate on the various ways humans have slipped the surly bonds of Earth. For those who want the big picture, there are daily shows in the Langley Imax theater and Einstein Planetarium.

TIP: This is the world's most popular museum and it gets crowded quickly. Decide in advance which of the 23 galleries you want to see most and hit them hard and fast. Get your Imax tickets early; performances often sell out by noon. THE ANACOSTIA MUSEUM opened in 1967 to interest and attract members of Washington's minority communities. First housed in an abandoned supermarket, the museum now stands on an airy, wooded knoll, with spacious grounds that often resound with concerts and festivals. It's no longer known as the Anacostia Neighborhood Museum, but maintains the homey atmosphere the original name implied; children are not just tolerated here, they are cherished. Exhibits focus on the triumphs and trials of members of American minority communities from slavery days to the current wave of immigration from Cuba and Latin America and draw heavily on personal items handed down through the generations.

TIP: Add your name to the museum mailing list in the lobby, and they'll keep you alerted to the African American, Caribbean and Latin music, food and craft festivals the Anacostia sponsors. THE RENWICK GALLERY offers splendid reassurance that the era of the great American craftsperson isn't over. The Renwick, a division of the National Museum of American Art, is a showcase for traditional crafts such as weaving, woodworking and glass and metal sculpture. It's also a theater for those who push the envelope, exploring the possibilities of computer-aided design and space-age materials. The wide-ranging and imaginative shows mounted here undermine the traditional distinctions between the fine and the decorative arts, and between the artist and the artisan. The main thing that distinguishes the Renwick from other contemporary art museums is that most of the objects shown here are as wonderfully well-made as architect James Renwick's splendid 1861 building (which originally housed the Corcoran Gallery of Art).

TIP: The gallery at the head of the grand staircase is a matchless evocation of a Gilded Age salon. THE NATIONAL MUSEUM OF NATURAL HISTORY is the one they have in mind when they call the Smithsonian "the nation's attic." Until 1969 it was the National Museum, and its collections include the majority of the 140 million things that the institution, at last count, thinks it owns, including 4 million moths and butterflies and 65,000 fossils from the Burgess shale. The place is just one gee-whiz after another, from the huge stuffed African elephant in the Rotunda to the giant mastodon and Irish elk skeletons in the Ice Age section to the humongous whales and dinosaurs. Natural History's full name includes "and the Museum of Man," which is why the exhibits embrace not only human evolution but the development of civilization. Since its beginning the museum has sent explorers to the far corners of the Earth. This summer's expeditions will include a deep-sea search for giant squids.

TIP: Natural History proudly asserts that its fabulous Hope Diamond is "the most popular single museum object in the world," and the waiting line sometimes stretches nearly full circle around the Rotunda. To get a glimpse of the accursed bauble without spending upward of a half-hour in line, the museum recommends arriving by 10:30 or after 4. THE FREER GALLERY OF ART is a monument in stone to the beauty of art and the stubbornness of man. The building and its Asian and American art objects were forced on an unprepared Smithso-nian in 1906 by Detroit industrialist Charles Lang Freer and President Teddy Roosevelt. Part of the deal was that nothing may ever be added to the American collection, nothing may ever be sold or lent from either the American or Asian collections, and that no outside objects may be exhibited with either. The Asian collection has more than tripled to about 26,500 objects; the static American collection increasingly reveals the fallibility of Freer's judgment. The centerpiece of the 1921 Italian Renaissance building is James Abbott McNeill Whistler's ornate Peacock Room.

TIP: The Freer is seldom crowded; it's the place to flee with the family when the crush on the Mall gets to y'all. THE NATIONAL MUSEUM OF AMERICAN ART, which shares the Old Patent Office Building with the National Portrait Gallery, used to be the National Collection of Fine Arts. The name was changed in 1980 to reflect a new emphasis on folk art, of which the outstanding example is James Hampton's foil-and-light bulb "Throne of the Third Heaven of the Nations Millennium General Assembly." The museum's collection is broad and deep but uneven, reflecting its mission to seek out representative -- not necessarily the finest -- American art. Still, the museum has an excellent collection of Washington Color School paintings and, on permanent and stunning display, a trio of Thomas Moran's grand and giant landscapes of the canyons of the Yellowstone and the Colorado.

TIP: The courtyard is one of the most pleasant outdoor eating spots in Washington; its Patent Pending Cafe is okay, but pricey; you may want to pack your own lunch. THE NATIONAL ZOO, which started as animal pens on the Mall in front of the Smithsonian Castle, moved to Rock Creek Park in 1891. Long a classic capture-and-cage-them animal prison, the zoo in recent decades has become a world leader in zoo reform and a world center for studying, breeding and "rewilding" endangered species. The zoo has progressed from attempting to house its animals in naturalistic habitats to re-creating an actual ecosystem; Amazonia, the rain-forest exhibition, has just about everything except the fabled Amazon mosquitoes. The Think Tank, an open-ended experiment exploring how primates think and socialize, employs aerial pathways offering our distant cousins various choices of where and with whom to sleep, play, eat or simply pass the time. The most popular zoo resident still is giant panda Hsing-Hsing, widower of Ling-Ling.

TIP: Wear a khaki shirt or jacket -- the animals may take you for a zoo staffer and come close to see what you've brought. THE ARTS AND INDUSTRIES BUILDING opened in 1881 to house artifacts from the 1876 American Centennial Exhibition in Philadelphia. This red-brick neighbor of the Smithsonian Castle houses an eclectic mix of centennial Americana and traveling and experimental exhibitions. The vintage elements of the collection, renewed for the 1976 Bicentennial, re-create the cluttered, industry-adoring atmosphere of the original museum; machines and furnishings that then were the latest thing now are wonderfully quaint. Exhibits in the South Gallery are devoted to African American history and culture.

TIP: If the kids get cranky, send them outside to the carousel. THE ARTHUR M. SACKLER GALLERY tunnels under a roadblock that had kept the Smithsonian's Asian art collection scattered and isolated for nearly a century. The underground Sackler connects to the Freer Gallery, whose founder specified that his collections could never be lent or displayed with other objects. Other Asian objects owned by the Smithsonian had to be housed here, there and everywhere. The Sackler, gift of a similarly enthusiastic but less narcissistic collector, is free to lend and borrow. Its crown jewels are the magnificent ancient Indian and Persian art and illuminated manuscripts assembled by Parisian jeweler Henri Vever.

TIP: The small "focus" gallery next to the gift shop never fails to offer intriguing insights into the exotic art and complex history of Asia. THE NATIONAL MUSEUM OF AFRICAN ART may be underground, but its masks, sculpture, ornaments and other objects shed lovely, lucid light on the arts and cultures of the so-called Dark Continent. The museum was created in 1964 by Warren Robbins in a Capitol Hill town house once occupied by Frederick Douglass. Robbins, a former Foreign Service officer with no personal fortune, used persuasion, persistence and consummate grantsmanship to build the museum to national status; it merged with the Smithsonian in 1979 and moved to the Mall. Robbins used the storyteller's technique to explain artifacts, and his successors have wisely maintained his methodology; a visit is always as entertaining as it is informative, and there are terrific programs for children.

TIP: The gift shop is one of the best in Washington. THE NATIONAL POSTAL MUSEUM is a stamp collector's dream. Located in the noble marble City Post Office next to Union Station, it displays some 60,000 U.S. and foreign stamps, drawing philatelists from all over the world. The museum houses a working post office with a broad selection of recent issues. Permanent displays include a spooky re-creation of a dark and gloomy Colonial post road, a horse-drawn express mail coach and a railway post office car. Most moving, however, are the cards and letters that illustrate the joys and hardships of separation, immigration and the westward movement; in this age of telephones and e-mail it's hard to conceive of how central the mail service once was to the lives of most Americans.

TIP: This is the one place in town that hunters can count on finding "duck stamps," the migratory waterfowl hunting and conservation stamps that hunters are required to buy but post offices are not required to stock. THE NATIONAL MUSEUM OF AMERICAN HISTORY is the Smithsonian's WalMart. Founded as the National Museum of History and Technology, it changed its name when it changed its emphasis from celebrating the great men of politics, science and war to exploring the experiences of ordinary Americans. In recent years this has led to exhibits such as "Field to Factory," examining how the economic servitude that replaced slavery for African Americans in much of the South led to migration to northern industrial cities, and "A More Perfect Union," exploring the imprisonment of Japanese Americans during World War II. The museum also houses pop-culture icons such as Don Garlitz's dragster and the ruby slippers from "The Wizard of Oz." But the enduring favorites are the Star-Spangled Banner, the First Ladies' inaugural gowns and the mighty No. 1401 Pacific locomotive, around which the building was built.

TIP: This museum is almost always crowded, but has many nooks and crannies, especially on the top floor, that are full of neat stuff. Try to find Civil War Gen. Philip Sheridan's (stuffed) horse. THE HIRSHHORN MUSEUM and Sculpture Garden, like the Freer, is the result of a collaboration between a rich man and a powerful one. Many of the world's museums coveted the mostly modern artworks amassed by junk king Joseph H. Hirshhorn, but Smithsonian Secretary S. Dillon Ripley was the one who brought home the Bacons, along with the Moores and Matisses, the Daumiers and the Davises, the Picassos and Pollocks. The distinctive, donut-shaped museum opened in 1974 and its endowment and circle of supporters have made possible the continuing exhibition and collection of cutting-edge art.

TIP: Don't miss the sunken sculpture garden on the Mall side of the museum. HANDS-ON OFFERINGS

The Discovery Room at the National Museum of Natural History, which opened as a "temporary experiment" in 1974, began a trend of visitor involvement that has spread throughout the Smithsonian and the rest of the museum world. No longer is everything behind glass -- "please touch" is the order of the day. Most such centers are aimed at youngsters in hopes of igniting a spark that may grow into a lifelong understanding and appreciation of science and history. For those who prefer to be non-interactively wowed, there's the Imax theater and planetarium in Air and Space, and live children's theater in Arts and Industries. Hours and admission requirements vary, so check the Smithsonian recording before you go: 202/357-2700 (TDD: 202/357-1729). MUSEUM OF NATURAL HISTORY

Discovery Room: Here kids get to feel animal fur, find fun wildlife facts and gaze at stuffed animals. One of the enduring attractions is the "hands-in" mystery box, a series of portholes into which one reaches and tries to guess, by touch alone, what's inside. It may be bones, beaver fur, a seashell or whatever other delight a docent has chosen. First floor.

O. Orkin Insect Zoo: At this zoo -- named after its principal benefactor, a company dedicated to the extermination of insects -- creepy-crawlies infest, ingest and digest each other and creep and crawl (under close supervision) over willing visitors; the perennial stars are the hideous, harmless tarantulas. Second floor. MUSEUM OF AMERICAN HISTORY

Hands On Science Center: The science center does a booming business in experiments with everything from battery building to DNA crime solving. Youngsters from kindergartners to teenagers are presented with puzzles and phenomena deftly delivered by delightfully diverse docents, or may investigate such things as electric circuits and background radiation on their own. First floor.

Hands On History Room: Here, kids can sort mail, pedal a penny-farthing bicycle, make old-time music and pry into a pre-Civil War rural peddler's pack, among some 30 historical experiences. Second floor. (Tickets, free, required on weekends.) AIR AND SPACE MUSEUM

How Things Fly: Scheduled to open Sept. 20, this hands-on center will feature a supersonic wind tunnel where visitors can make real shock waves, a Cessna you can climb into and operate the controls of, and some 50 interactive stations demonstrating such aeronautic esoterica as fly-by-wire, overseen by docents young enough to understand such stuff. In Gallery 109. THE NATIONAL ZOO

Zoolab: Children ages 4 to 7 will enjoy this classroom-size space in the Visitors Center (formerly known as the Education Building). There are displays on animal families and other zoo-logical topics. The walls are furnished with animal skins that hang low enough to be touched by tykes. Attendants stand by to answer questions.

The Bird Resource Center: The center, in a coat room-size cranny at the rear of the bird house, has a few activity boxes for kids. The topics of these are eggs, feathers, wing spans and bird trivia. For adults and older kids, attendants answer bird-related questions ranging from the practical (What kind of bird feeder should I put up?) to the trivial (How many birds are in the National Zoo?). NOW SHOWING . . . * SAMUEL P. LANGLEY THEATER: The Langley Theater this month inaugurated "Cosmic Voyage," the most ambitious yet of its large-format Imax films (projected on a 55-by-75-foot screen), which joins the long-standing lineup of "To Fly," "Blue Planet," "The Dream Is Alive" and "Destiny in Space," along with various travelogues, documentaries, and more-or-less-natural nature shows. Admission to the 486-seat theater is $4 adults and $2.75 for those between 2 and 21 and over 54. For information, call 202/357-1686. * ALBERT EINSTEIN PLANETARIUM: "The New Solar System," shown every 40 minutes from 11 a.m. through 5 p.m., except for a special free local astronomy show each day at 3, explores the ever-deepening and expanding cosmos revealed by radio astronomy, computer enhancement and the Hubble space telescope. In the astronomy show, "The Stars Tonight," visitors can brush up on the major stars, constellations and satellites visible in the Washington region. Admission to "The New Solar System" is $4 adults and $2.75 for those between 2 and 21 and over 54. For information, call 202/357-1686. * DISCOVERY THEATER: The Smithsonian Associates presents shows for toddlers through teenagers in the Arts and Industries Building. The range is from "The Little Red Hen" through puppetry to "The Legacy of Anne Frank." For information, call 202/357-1500. From Your Basement to the Nation's Attic

Many of the items in the Smithsonian's vast collection came from regular citizens who were inspired to donate a work of art, a bit of history -- or a piece of junk. Should you attempt a donation? Probably not.

If you collect stamps, for instance, Uncle Sam almost surely can't use them. "We are very selective in what we take here," says National Postal Museum director James H. Bruns. "Stamp-wise, we only accept philatelic specimens that represent significant voids in our collection." He's talking about a 16 million-stamp collection, so significant voids are few.

But if you collect, say, entire postal delivery wagons, you might find a receptive ear at the museum. Bruns says his wish list includes certain wagons used in the 1880s and in the 1920-1940 era. He also has been hunting for whistles used by 1920s mail carriers, civil defense decals that were made for display on 1960s mail trucks, and mail carriers' pith-helmet-style hard hats (original specimens in gray or brown, please).

At other Smithsonian museums, the story is much the same: short lists of extremely coveted artifacts.

If you think you may have such an item and are willing to donate it, make the offer by mail. Call 202/357-1300 to get the name of the Smithsonian division that would most likely consider your offer. Then send a picture or sketch of the object, along with its dimensions. If possible, include such information as patent dates, patent numbers, maker's name, model number and label information. Paperwork such as a sales receipt is always helpful.

Don't ask for an appraisal. It's a strict Smithsonian policy not to put a dollar value on any donated object. As for any income tax deductions, that's between you, a commercial appraiser and the IRS. DID YOU KNOW?

* It took two taxidermists 16 months to mount the African bush elephant on exhibit in the rotunda of the National Museum of Natural History.

* The two most common questions asked at the information desk of the Museum of American History: Where are the bathrooms? Where are the ruby slippers?

* Top three sellers in the gift shop of the Museum of American History: "M*A*S*H" dog tags, a packet of D.C. postcards, freeze-dried "astronaut" ice cream made by Luvy-Duvy Corp.

* The earliest painting in the National Portrait Gallery is of Pocahontas, painted by an unidentified artist after a 1616 engraving (also in the collection) by Simon van de Passe.

* The largest rooftop garden in the world is the Enid A. Haupt Garden atop the underground complex containing the Sackler Gallery, Museum of African Art and Ripley Center.

* The coat worn by singer Marian Anderson during her famed Lincoln Memorial performance is in the Anacostia Museum collection.

* During World War II, the huge flag that inspired the "Star Spangled-Banner" was wrapped in tar paper and hidden in a Virginia cavern until the threat of a foreign invasion passed.

* Alexander Graham Bell orchestrated the transportation of James Smithson's body to Washington from its original burial site in Italy.

* During the Civil War, President Abraham Lincoln once climbed the 145-foot north tower of the Smithsonian Castle to watch Confederate troop movements in Alexandria.

* After donating the Spirit of St. Louis to the Smithsonian in 1928, Charles Lindbergh asked for a chance to sit in it again. A ladder was provided and he climbed to the cockpit and sat alone for a few hours.

* Objects in the Smithsonian's collection that have been stolen over the past two decades (and recovered in most cases) include a machine gun, a gold-and-diamond snuffbox, a bicycle racing outfit and George Washington's false teeth. CAPTION: Aretha Franklin (left), the American Indian Dance Theater and Trisha Yearwood are among the performers helping the Smithsonian commemorate its 150th birthday this weekend. CAPTION: SMITHSONIAN CASTLE CAKE CONSTRUCTED BY PATTY KOSCIUSZKO COLLETTE, PATTY CAKES INC. CAPTION: Smithsonian Castle cake constructed by Patty Kosciuszko Collette, Patty Cakes Inc.