Rolland Hower doesn't mind if someone touches his brain -- even a 10-year-old. Well, it's not exactly his brain, but just one of many freeze-dried specimens the chief of the National Museum of Natural History's exhibits research laboratory has lying around. And it's perfectly fine for a kid to touch it. "It won't hurt the brain and won't hurt him," says Hower while smiling at the 10-year-old and encouraging visitors to explore, reassuring them. "There's nothing explosive, nothing breakable." You won't find Hower or his freeze-dry lab in any of the main exhibit halls of the beautiful, high-ceilinged Natural History building. They are tucked away above a metal staircase, past some rolled-up carpets in the wide hallways behind the exhibits area. And this modern-day Merlin of the Smithsonian is just one of many good secrets Washington's museum have behind the scenes. Above, below and behind the collections on display is a world of backstage activity. Collecting, storing, conserving, repairing and mounting exhibits is a continuous process, one not usually on view. But it is possible to slip backstage, as it were, and catch a glimpse of the researchers, conservators and scholars at work, as well as to view some of the majority of museum collections not on display. On these trips, you will get to meet more than guards who admonish you not to touch. At times, you'll be encouraged to touch, certainly to ask questions. As noisy as the crowded public rooms of some museums are, the private backstage ones are quiet, full of opportunities to sneak a peek at future items slated for exhibit. A look at stored treasures and a share in the excitement of how items are reconstructed are other pleasures. Here, then, is a field guide to what is not on display in Washington's museums. QUILT TOUR: TUESDAY AT 11. National Museum of American History, 14th and Constitution NW. By appointment: 357-1889. This Tuesday morning, Frank Fram of Wheaton is one of the few men in a group bound for the fourth-floor storage rooms of the National Museum of History and Technology. Fram, his shirt adorned with a special visitor's pass, is on his way to see the museum's heirloom quilts.

"I've got a wife here," says Fram, gesturing to the front of the small group. "But," he goes on, "I do some weaving. I'm interested in almost all textile things."

It's not hard to see why. Quilting is history worked into cloth, stitch by tiny stitch. Tradition. And within the province of the fourth-floor storage area are quilts that covered marriage beds, trousseau linens, patterns that traveled from one part of the country to another, friendship handwoven at quilting bees in wool and calico.

Although quilting has been practiced for thousands of years (even soldiers of the Middle Ages wore quilted coats under their armor), the bulk of the museum's 300 quilts range from the 18th century to early 1900.

Most of the quilts are American, though even the curators do not profess to know the origins of all the objects. Where detail is lacking, beauty suffices.

From sliding racks come quilts of applique, piecework, embroidery, patterns representative of regional America. Jumbled, odd-sized patches sewn together in no particular pattern are "crazy" quilts, remnants of a Victorian rage.

Americana is sewn in. Flags and eagles, cornucopias of fruits, pieced medallion-type chintzes and clamshell designs are reminiscent of a fledgling new world. Twill woven coverlets, album quilts and printed counterpanes bespeak small towns and country places.

A "Wreath of Roses" quilt, stitched in Pennsylvania and embroidered with the date 1849, might have kept away the draft from that winter. Another, indigo glazed wool, received its shine in the same manner wool pants would if pressed too long with a hot iron.

Geometric and floral patterns lend themselves to stories, events and customs.

In days past, a young maiden to be married had elevan quilts in her trousseau. The twelfth, a white one, was made for her wedding day. Displayed are finely stitched examples of wedding quilts, some plunged in boiling water to produce puckered effects and bas-relief patterns.

Many needlewomen signed their creations. In reverie, it's easy to speculate on the life of Marget Nowlan of Ohio, who, in 1822, stitched her name to a basket of flowers in the center of a soft green quilt. In the spacious, windowless white storage room, stacks of boxes marked "lace pillows, garments and trimmings, dress fabrics and trims, wool blankets -- colonial types" reach ceilingward. Even the hallways are a treat: Framed pieces of old, rare lace hang next to an elaborate embroidered wall hanging done by Mrs. Theodore Roosevelt.

And then there's the THIMBLE COLLECTION.

Generally, this hodgepodge of oddities and beauties created to protect sewing fingers reposes in a fourth-floor hallway. Currently, it's on view as part of the "Nation's Attic" exhibit. When it returns, one can contemplate privately the hundreds of gold, silver, china, steel, plastic, bejeweled or imitation fingernail thimbles by making an appointment.

It's advisable to call one or two months in advance for reservations. Space is limited and group reservations are not taken.

PRINT STUDY ROOM, DEPARTMENT OF PRINTS AND DRAWINGS, National Museum of American Art, Eighth and G NW. By appointment: 357-2593.

More than 24,000 paintings, sculptures, prints and drawings make up the collection: Two hundred years of American art in the oldest national art collection in the country, antedating even the Smithsonian.

So, after seeing the beautiful paintings and objects on view, you may be tempted to skip what's not on display. It will be a loss if you do.

"Because we are a public museum, our collection should be open to everybody," says Margery Byers, chief of the museum's office of public affairs. That includes what's not on the walls.

New vision may be triggered by viewing your favorite painting or sculpture not on display. Ask for a special appointment to see it among the thousands in storage.

More enticing is the fact that the museum's Print Study Room on the first floor is open to the public by appointment. In this room, black boxes filled with the finest examples of the art of printmaking are stacked to the ceiling. The boxes are categorized by artist, making it easy to spend your time with favorites.

"Prints can only stay up for a relatively short time because light can be damaging to them," says Janet Flint, curator of prints and drawings.

Inside this quiet, art-hung room dominated by a conference table with modern, comfortable chairs, visitors can sift and probe through boxes of artists' work, not separated by glass or crowds.

"That's the way prints are supposed to be viewed," says Flint.

The collection is primarily 20th-century. Representative is work by Stuart Davis, Raphael Soyer, Washington's own Jacob Kainen and a particularly delicate George Bellows etching of his wife, Emma, entitled "The Black Hat."

In addition, there is a sizable collection of WPA prints, including many by Will Barnett, done in a style unlike his current work.

Staff members will instruct you on the proper handling of prints for private viewing, and then you're on your own. Catalogues of artists' work are available in the museum's library. A self-guided tour, this one.

STORAGE AREA TOUR: FREER GALLERY OF ART, 12th and Jefferson Drive SW. By appointment: 357-2104 If you enjoy the Freer collection of some of the best Oriental art in the West -- if seeing 19th- and early-20th-century American prints and drawings in an elegant small Renaissance building appeals to you -- you will love the hidden or stored parts of the Freer Gallery of Art collection. In basement storage rooms and restoration areas, there's as much excitement as in the upper galleries -- and more to see.

Part of Charles Lang Freer's charge when he donated his fine collection of Orientalia to the Smithsonian was that it never leave the gallery. Since only 10 percent is on public view at once, there remains much to see.

A guided tour will take you to revolving racks of James A. McNeill Whistler works. The collection of prints by Whistler is said to be the largest outside of Glasgow. Quite as important are works by Childe Hassam, Winslow Homer and Thomas Dewing. These were included by Freer to show the bridge between Eastern and Western art.

Eight storage rooms bulge with bounty, from Chinese ceramics (Neolithic period through the Chi'ing dynasty) to a storage room filled with jade carvings and bronze ceremonial vessels.

"Anyone can request to see by appointment anything not on display," says Sarah Newmeyer, gallery administrative officer.

It's worth making an appointment. A Chinese calligraphy collection, from the Chin dynasty (in the third century A.D.) through 20th-century Ch'ing, can be seen by request. Ancient scrolls and wall hangings depicting royal journeys or stories by court painters are poetic images.

Rooms are crammed with cases of ceremonial objects, old Imari, Seto Ware, Raku Ware, gilt bronze statues and Buddhist figures.

Conservators and researchers are quietly at work among this store of riches.

A beige-and-white, sun-filled room is the space where two masters of hyogushi, the Japanese craft of restoration, ply their trade. In this age-old tradition, paintings, scrolls and screens are remounted, cleaned and mended, and wrinkles removed. Sitting crosslegged or kneeling on straw mats, the men use seven different kinds of paste to restore deteriorating papers and silks.

In another part of the basement, the ravages of time are combatted by conservators in the technical laboratory, where walls of chemicals remind the visitor of a pharmacy. To light the past, ancient objects are analyzed with modern methods and materials. In a mundane sense, it is where the Freer experts tell jade from plastic.

Staff members will answer questions during the tour and there is a chance to see the small but exquisite collection of hand carved furniture in offices and hallways.

EXHIBITS RESEARCH LABORATORY, NATIONAL MUSEUM OF NATURAL HISTORY, Tenth and Constitution NW. By appointment: 357-2644. Who can blame Rolland Hower for liking his job? He's stopping time surrounded by snakes, squirrels, bluebirds, splinters from Civil War blockade-running ships, a woolly monkey, an armadillo and white-feathered cockatoos. The animals appear in suspended animation, realistically positioned. Each is exactly as it was in life, except for replaced eyes. Each is freeze-dried.

Certainly the best day to visit this silent zoo is when Hower opens one of the two freeze-dry vats that take up most of the laboratories, and adds more birds, fish, beasts and insects to counters already filled with specimens looking poised to strike or fly.

Hower, one of only two people in this country with a doctorate in cryobiology, pioneered this method of preserving animals, virtually making taxidermy obsolete for exhibits. Now older exhibits are gradually being replaced with freeze-dried specimens.

Zip -- into the vats go bats, alligators, birds, even an eight-foot dragon (now on display in the reptile exhibit). Moisture is slowly removed under vacuum, preserving the animal intact for exhibit or study.

"We're the last of the alchemy labs. We do just about anything nobody else wants to or can," says Hower, who needs no time to warm to visitors or his subject.

A visit here -- and Hower prefers to call them "unofficial visits" rather than tours -- will glean short physics lessons and philosophy.

"This is what the bird would look like with his clothes on," says Hower pointing to a textbook picture of the Great Frigate Bird whose skeleton is being recontructed on a counter.

After noting that this is the bird who sweeps down and picks up 90 percent of baby sea turtles all the time."

And don't think Hower is going around gathering these examples for exhibit on his own. No indeed.

"We don't collect. We depend on picture windows, automobiles and television towers for our specimens. It's an indiscriminate mode of collecting, at best," he adds: "TV towers could care less what flies by."

Anyone who ever put fireflies in a jar will find something wonderful in this lab. Kids, whom Hower admonishes to remember to get into some mischief during childhood, will get a chance to see items destined for the children's discovery room. Hower may even tell you about his friend Princess Redwing, "a very charming lady of 85 years old." But call first.

"If I'm up to my knees, obviously I can't devote much time to visitors. But our whole charge is the diffusion of knowledge and we feel that responsibility." PAUL E. GARBER PRESERVATION, RESTORATION AND STORAGE FACILITY, Old Silver Hill Road, Suitland. Guided tours Monday through Friday at 10; Saturday and Sunday at 10 and 1. By appointment; call two weeks in advance: 357-1400. Bill Reese is building a powered hang-glider in his living room, which helps explain why he used to spend a lot of Saturdays at the Paul E. Garber Facility doing what he loves best -- restoring airplanes.

"Everybody who works in this shop is an airplane fanatic. I wouldn't trade my job for any other in the world, except to fly," says Reese, who during the week works in the collection management division at this Prince George's County adjunct of the National Air and Space Museum.

In 24 hangar-type buildings are ghosts of skies past, in varying states of repair and restoration.

"Sometimes you get a real spooky feeling in these planes. Some people lived in 'em and some people died in 'em," observes Reese.

Discovering how they originally looked and restoring them to that state is the work of this facility. Modern jigsaw puzzles, planes are dismantled piece by piece and reassembled.

Restorers travel the world to authenticate a plane's markings. Custom fabrics are commissioned to duplicate originals exactly. The painstaking work of authentication, preservation and restoration goes on in the fabric, chemical, welding, wood, sheet-metal and machine shops of Building 10, just so years from now people will know exactly what Corsairs, F4 Phantom Fighters or KC-97s were -- right down to original fabrics and instruments.

"One hundred and fifty years from now, they can take it apart and see how we did things in 1980. This is for our children and our children's children," says Reese.

What they will see in the future, you can see now. Not far from the neon clutter of shopping centers, rows of planes sit silently recalling eras past.

There's the "Jenny," a World War I barnstorming favorite of the 1920s. And "Bedcheck Charlie," the Korean War nemesis that tried unsuccessfully to bomb hospitals each day at 5 o'clock.

John F. Kennedy's campaign plane, the "Caroline," reposes between two buildings. And, despite rumors that the "Enola Gay,", which that carried the atomic bomb to Hiroshima, is under wraps, it is not. Too large to be fully assembled, its silver fuselage and wings loom from the back of a dimly lit building.

Even Hollywood gets into the act. The Waldo Pepper-type plane Robert Redford flew is here, as is the model for the mother ship in "Close Encounters of the Third Kind."

There is also a genuine flying saucer. Reese says it was built for the United States Air Force by Canada.

Planes are everywhere, even hanging from rafters, like the early French bomber with an opening in the floor so the bombadier could drop the bomb held between his knees.

The man responsible for most of this assemblage is Paul E. Garber, 82-year-ole historian emeritus of the National Air and Space Museum, but public demand has played a part, too.

A docent-led tour will take you past shops and storage areas, plus wherever else your imagination may lead you.

During one tour, two young boys, fascinated by the control panels of a KC-97 trainer, scrambled into the cockpit. Without batting an eye, a docent called to them: "You can go in there, boys. Go in and fly it away."