WASHINGTON has almost no end of world-class free museums. They're a magnet for thousands who descend on the mall every weekend, offspring in tow, to walk the marble paths to enlightenment.

But where to start? What to see? There's such an embarrassment of cultural riches that we tend to gorge indiscriminately. Sit outside the entrance to any museum and you'll see the unmistakable signs of museum indigestion. Grownups stagger out, eyes glazed, with little kids puffy-eyed from wailing (there's such a satisfying echo in those cavernous museum halls) trailing crankily behind.

The sensible thing is to plan your attack in advance. When you walk into a museum you should know pretty well what direction you're going to take. Have some idea of which exhibits will most likely appeal to your pre-schooler, your 5- to 8-year-old or your 9- to 12-year-old. (Any older and they already know what they want to see and wouldn't listen to you anyway.)

Herewith, the first in an occasional series of manageable and fun museum itineraries geared to each of the above age groups' level of understanding, attention span and physical stamina. We'll throw in some factual snippets to enable parents to appear at least a little more knowledgeable than the exhibit captions. And we'll give you hard data on where the water fountains and bathrooms are. NATURAL HISTORY MUSEUM

If you've ever climbed the 22 wide marble steps from the Mall and walked through the imposing pillared portal of the National Museum of Natural History on a weekend afternoon, you know what chaos is. After your eyes adjust to the dimness and you find a safe spot out of the way of strollers, you'll see that there are at least six directions you can take from the massive main rotunda -- including back out, if it all proves too much for you.

Fear not. The first course of action is to aim for the main information desk (at 4 o'clock on your right) and pick up a brochure. Decide what you want to see and plot your route on the detailed floorplans provided. Also ask for one of the question-and-answer discovery brochures designed to give children a thematic guide to subjects such as shelter, ceremonies and celebrations, masks and headdresses and money. In conjunction with special shows, the museum also creates brochures that lead kids on a treasure or scavenger hunt through the exhibit. Finally, walk over to the African bush elephant lording it over the entranceway and check out Today's Special Program notice in the brass stand in front of the 13-foot giant, for times of films, talks or guided tours.

The crucial ingredient of a successful museum visit lies in not overdoing it, advises Laura McKie, the museum's acting assistant director for education. "It's better to leave the kids wanting more than trying to do everything in one visit." And since we lucky people live here and can come back again and again, we can afford to be selective.

McKie also talks about "framing" your visit by asking questions such as: What do you think you're going to see? What is natural history anyway?

"Basically," says McKie, "natural history is about the things you can see. It's a way of looking at the world and the people who live in it."

At the end of your visit, ask the kids what they liked best, what was scariest, what they would come back to see again. Even the museum itself can become a subject for discussion. "Little kids are very impressed by the building," says McKie. "So ask them questions like: Why do people build museums to look like this? Do you think this exhibit is old or new? Try to get across how a museum represents an attitude toward preserving things and how those attitudes change."

For instance, many of the stuffed African specimens in the Mammal Hall were bagged by Theodore Roosevelt on safari more than 80 years ago. Can you imagine a healthy pride of lions being shot and stuffed for display in our conservation-minded era?

Another important factor in a successful family museum visit is what the parents put into it, says McKie. Just reading off the captions under an exhibit isn't enough. You've got to translate the information into terms children can understand and actively engage their interest.

"Learning to use the museum purposefully is the key," says McKie.

With that in mind, McKie has suggested three itineraries geared to age group and to school curricula. To make the most of your visit, try to arrive early -- the doors open at 10 every day but Christmas. Fall is ideal; the tourist tide has ebbed and won't rise again until the floods of April and May when it gets so crowded that even the museum gives up on trying to conduct any group tours. PRE-SCHOOLERS

McKie recommends that pre-schoolers spend no more than an hour in the museum -- including a trip to the bathroom. This allows enough time for a good long look at the dinosaurs, a refreshing dip into Sea Life and a walk past the mammals.

Start in Dinosaur Hall (to the right of the information desk) heralded by an orange banner with a mauve dinosaur. Zip around the fossil wall and you come up against Diploducus longus, 90 feet of undulating skeleton looming high overhead. Slightly less intimidating is the fleshed-out 1904 model of a stegosaurus to the right, a non-threatening vegetarian with zigzag plates, a tiny head and a rather cute little face.

You might want to shepherd little ones past the fearsome antrodemus skeleton a little farther along on the left in the center pit -- this was a flesh-eater with a much larger head and mean-looking teeth and claws -- to the safe haven of "Life in the Jurassic," a mini-diorama on the right-hand wall. Toy-size dinosaurs roam a sparsely vegetated plain, providing a useful scale to compare sizes of the dinosaurs that lived in this middle era. You can ask youngsters to try to match the models with the life-size skeletons.

On a recent look into the diorama, I heard one pre-schooler blithely pipe up, "Mommy, we were bigger than them!" -- despite considerable evidence to the contrary looming above and all around her. But mom, distracted by helping dad set up a photograph, automatically murmured "Yes, dear" and the little girl happily wandered on, secure in her mistaken conclusion.

Scoot around the long-jawed reptiles at the end of the hall and double back along the other side, past the Paleo Lab, a glassed-in workshop in which technicians are painstakingly uncovering a dinosaur bone trove, to another diorama called "The Eleventh Hour." The time is 70 million years ago, when dinosaurs were at their height and greatest variety, and plant life has branched out. You can ask kids what differences they notice in the animals and vegetation.

Heading toward the exit you'll pass the black cast of the huge head of a Tyrannosaurus rex with six-inch incisors. This is definitely thrilling, especially if you hold a little one up to get a good close look at the size of those teeth. Just a little farther along on the right is a seven-foot Brachiosaurus leg bone you can touch. And there's a sketch of this enormous dinosaur -- taller even than diploducus -- showing where the bone fits. The last exhibit on this side of the hall is titled "The Baby (?) Dinosaur from Montana." In the case is a heifer-size dinosaur skeleton which may be a small adult or a baby. Ask the kids what they think. And before you move on, turn around and cast a glance high up at the opposite wall, where hang the skeletons of Edmontosaur and Albertosaur, two neglected dinosaurs too lofty for most visitors to notice.

From Dinosaur Hall, run the gamut between the charging elephant and the stuffed Indian tiger eternally poised to pounce and head for Sea Life. (Look for a blue banner with a fuschia whale.) It's like diving underwater -- the hall is dim and a little scary, especially with the life-size 92-foot blue whale hanging from the ceiling. If the grinning mammal proves too much for young sensibilities, you can duck into the brighter alcove on the left to see two marine ecosystems in action.

One wall of water behind glass gives you a fish-eye's view of a sub-Arctic coast, complete with intermittent wave action and 50 to 75 living creatures. On the opposite wall is a tropical coast shimmering with iridescent fish darting in an out of living coral formations. There are 400 to 500 species in this tank and you can make a game out of who can spot the most. It's not as easy as it sounds -- most are well camouflaged and shy.

Alvin, a 3/4-scale model of a manned submersible, hovers around the blue whale near the ceiling and looks a bit like a cartoon character along the lines of Little Toot. Along the left wall of the Sea Life hall are comparatively static cases filled with shells and large-size models of minute sea creatures. But in the alcove to the left of Alvin, there's a fascinating creature kids will enjoy. In the third case from the left you'll find a model of a boxer crab, a pugnacious crustacean with a pinkish body and hairy legs who holds up two stinging sea anemones, boxing-glove style, in his front claws to fend off enemies.

At the end of the hall, there's an enormous stuffed walrus with a large sign announcing "I am a pinniped." At the base of the bewhiskered and betusked walrus is a video screen showing various other pinnipeds cavorting in the wild. There's a bank of phone receivers to supply the narration and kids love to pick them up even though the sound is usually garbled or non-existent. One little girl picked up a dead phone, listened pensively, said "Hello Grandma," looked satisfied and hung up.

To the right of the walrus is a water fountain with a climb-up step for thirsty toddlers. Wet your whistle amd then go back past the walrus and turn left into the Mammal Hall and walk back past the dioramas toward the main rotunda at whatever pace your pre-schooler's museum tolerance will stand. You'll pass gorillas, monkeys, an armadillo and a panda, lions, bats, beavers, squirrels and gophers and a cute little wallaby.

You're probably ready for a pit stop by now. The nearest restrooms are en route to the cafeteria (at 10 o'clock from the entrance), but these often have long lines. If you can hold on a little longer, take the escalator (12 o'clock) down to the ground floor to the spacious restrooms near the Constitution Avenue entrance. (If you have a stroller-bound baby, you'll have to take the stairs or the elevators, to the right or left of the rotunda. All the ladies' rooms have diaper-changing facilities but there are none in the men's rooms -- yet.)

If your children seem particularly taken by paleontology, drop into the Dinostore (opposite the main museum shop) where they can browse amongst a herd of stuffed, wooden, metal, plastic, rubber, foam, inflatable and paper dinosaurs for sale. The dinosaur cookie-cutters and baking molds are a big hit.

Then retrace your steps and leave the museum on the Mall side for a romp with Uncle Beazley, the friendly 25-foot-long fiberglass triceratops kids have been climbing on for more than 20 years. FIVE TO EIGHT YEARS

Plan on 5- to 8-year-olds spending about an hour and a half in the museum, including time in the museum shop and cafeteria. This tour starts at the de rigeur Dinosaur Hall, goes on to the Bird Hall, then past the mammals and into the Indian Halls.

This age group -- with years of Lego-building experience behind them -- is a little better able to appreciate the mechanics of the dinosaur display. For instance, they may be impressed by the fact that it took a whole year to collect and transport the bones from Utah back in 1923 and then seven years to assemble them. To see how time-consuming the paleontologist's work still is, take them to the glass-fronted Paleo Lab. The big draw here is that kids can work the controls of an overhead video camera to zero in on technicians laboriously scraping away solid rock to uncover the bones of Coelophysis, a small bipedal predatory dinosaur of 220 million years ago.

If you can tear them away from the video camera, leave Dinosaur Hall and head directly across the Rotunda into Bird Hall. The first diorama on the right holds an elegant group of emperor and Ade'lie penguins notable for their size and stately demeanor and for the fact that they were collected by a polar expedition under the command of Antarctic explorer Admiral Richard E. Byrd.

Along the left wall are cases filled with flocks of stuffed birds. The most colorful one's in the first alcove, a bevy of fantastically feathered peacocks, wild turkeys and birds of paradise. The next alcove focuses on nests and young, and has an endearing emperor penguin chick, downy soft but forever standing stiffly by his egg. The last diorama on the right is the best -- an ostrich mom and pop watching over just-hatched chicks. There's much clucking over the cute ensemble until the thought dawns that this whole family also was killed at the very threshold of generation, and by none other than Teddy Roosevelt, on safari in Kenya in 1910.

Around the corner to the right is a water fountain and, while waiting your turn to sip, take a look at the glass case of Large Birds of the African Marshes, which includes two shoe-billed storks -- also bagged by T.R. -- that wear Looney Tunes grins.

Now head down Mammal Hall, past the dioramas of caribou, moose and bighorn sheep, and be sure to pause at the black bear case which features two cuddly cubs and the real-world news that these papa bears don't help look after their young (in fact they may eat them, if they get a chance). Across the hall is a trio of hunting wolves. Though grim-faced, these doggy-like specimens should lay to rest any lingering bedtime fears of the Big Bad Wolf. Along the way, tell kids to look for the interesting little details that make these dioramas more lifelike -- like the stuffed prairie dog popping out of a hole in front of a herd of American Buffalo.

(A word of warning: The diorama glass is tilted to cut down on glare. This also means that a youngster charging from one to the next and leaning in to get a closer look can get an unexpected knock on the noggin. Heads up!)

At the end of the Mammal Hall is a welcome sign: Restrooms. The museum's popular hands-on Discovery Room is also here, but you'll want to make a separate visit to enjoy it properly. From here, turn right, into the hall titled Native Cultures of the Americas.

The dioramas here show their age -- most were created more than 75 years ago. They're rather stark and unlifelike but still intriguing. The first one, on the right, showing Carib Indians of tropical Guyana, offers the opportunity for a little etymology lesson. Ask your kids where the Indians slept. If they're sharp, they'll spy the skinny rope strung between two poles on the far right. Called a "hamaca" in Arawak, it's come down to us as the hammock.

Farther down on the right is a diorama showing a Hopi Indian Snake Dance in progress. This is when you're glad the figures aren't too true-to-life, especially the masked priest clenching a rattlesnake between his teeth. It's pretty impressive and all is explained in simple captions along the base of the case.

Ahead of you now are two tall totem poles, emblematic of Indians of the Northwest Coast. The nearby cases detail Indian ceremonies with artifacts and pictures, but even better is a video monitor showing a continuous program about a Kwakiutl potlatch ceremony in British Columbia. It's well done, the sound is intelligible and there is some wonderful black-and-white footage of a 1914 potlatch contrasted with a colorful modern-day celebration. And best of all, there's a small bench to plop down on and give your legs and back a rest (the kids can sit on the floor).

Continuing through the Northwest Coast Indian area, you'll pass cases filled with instruments of war -- wooden helmets, lethal-looking carved war clubs and, just opposite the giant Plains Indians tipi, a case containing two Indian scalps, taken by Cheyenne and Blackfoot warriors.

Around the glassed-in tall tipi, kids this age will particularly identify with the three children playing outside with a wooden hobby horse, dolls and a hoop-and-pole game.

More toys are on display in the Sub-Arctic section just past the tipi in a case titled Alaskan Eskimo Art. There's a box of toy animals exquisitely carved from wood, bone and ivory. In the Eskimo Homes and Furnishings case, kids can pick up pointers on how to build an igloo. And they're sure to recognize one Eskimo artifact here -- a short-handled snow shovel carved from wood and edged with ivory.

At the end of your Sub-Arctic expedition is a diorama of a sealskin-clad Eskimo family laughing heartily at a young boy pulling a puny seal out of an ice hole. Even the stuffed husky team seems to be smiling. The punchline is the diorama's title: "Call that a seal?" Gee, museums even have a sense of humor.

So leave 'em laughing as you emerge into the Rotunda. An immediate right turn takes you to restrooms, the Museum Shop and the cafeteria. NINE TO 12 YEARS

Nine- to 12-year-olds can probably last two hours in the museum, says McKie, as long as they help choose what they're going to see. Her suggested tour starts with dinosaurs, Sea Life and the Indian Halls, then moves upstairs to the Insect Zoo and earth sciences, in keeping with subjects this age group is studying in school.

In the Dinosaur Hall, kids this age will appreciate the captions, written with a sense of humor. For example, "The Better to Eat You With My Dear" jauntily details the eating habits of bipedal flesh-eating dinosaurs, complete with a sketch of a ceratosaurus munching on a camptosaurus' innards in a pool of blood. This should appeal to the most bloodthirsty pre-teen.

Opposite the working Paleo Lab is a geologic map of the U.S., color-coded to show where dinosaur bones most likely lie. Visitors are invited to find out "Could There Be a Dinosaur in Your Backyard?" (The answer for local kids is, not likely; there are a lot of dinosaur tracks but few bones in the early cretaceous rocks around Washington.)

Across the Rotunda in Sea Life, mention that the model of the blue whale suspended from the ceiling isn't quite accurate. It was constructed in 1963; since then, cetologists have discovered the model's throat is unnaturally distended. Budding marine biologists may be encouraged by the realization that there are still plenty of uncharted waters for them to explore.

And one exciting way to do it is on display here. The Hydrolab looks rather like an underwater RV, its galley stocked with familiar groceries and wetsuited lifesize aquanauts just returning from a walk on the ocean floor. There's a continuous video program behind the Hydrolab and detailed captions outline the work of this underwater lab but they may need some translation into terms kids can understand. One mother dutifully read all the captions word for word to her young son whose initial curiosity quickly faded into a bored silence.

Turn right at the end of Sea Life past the water fountain and past the mammal dioramas (kids might be surprised by the meek -- even sweet -- expressions on the grizzly bears' faces) to the Native Cultures or Indian Halls (another right turn). Of particular interest here, in the first alcove on the left, is an exhibit on the Jivaro Indians of Ecuador. You'll find a clinical but no less thrilling detailed account of How a Shrunken Head Was Prepared, from beheading to polishing, including samples, of course. And this terse summing up: "It took 20 hours."

Right next to the shrunken heads is a miniature diorama that puts an intriguing twist on our customary historical perspective. It's titled: Lucayan Indians Discover Columbus, October 16, 1492. Let the kids mull that one over.

Farther along near the Plains Indians tipi is a thought- provoking exhibit on Plains Indian Religion. An 1832 drawing by George Catlin shows a crowd of Sioux witnessing the torture of a young brave whose chest skin is being stretched by two hooks attached to a bent pole. It's titled "Sioux Self Torture" and the sketchy caption simply says: "A young man vowed to the sun that he would undergo self torture if he returned safely from a dangerous war expedition." That tidbit should send kids scrambling to the nearest library for more details on Sioux customs.

Just past the tipi is another diorama titled Blackfoot Indian Buffalo Drive. The action and the caption show and tell in fascinating and easy-to-understand detail how the horseless tribe stampeded buffalo over steep cliffs to their deaths.

Notable curiosities in the Sub-Arctic section include, in the Sea Hunting and Fishing Case, a remarkably high-tech sun visor made of wood and a diaphanous, waterproof seal-gut jacket that looks just like a patterned nylon shell. And in the Hunting Birds and Land Animals case, look for "An Ingenious Wolf Killer" -- a bent piece of sharpened whalebone embedded in frozen blubber. When the wolf gulped it down, the blubber melted and the whalebone sprang straight, piercing the wolf's innards.

On that edifyingly gruesome note, leave the Native Cultures Hall and take the stairs to the right up to the second floor; turn right at the top of the stairs and head into Bones, Reptiles and the Insect Zoo. You're aiming for the Insect Zoo but the animal skeletons along the walls make playing guess-whose-skeleton a natural game.

The stars of the Insect Zoo are the hairy tarantulas and scary scorpions. Kids can pretty much roam on their own here. There are a beehive and ant colony and a chance to pet an enormous live Madagascar Hissing Cockroach or a fat green Tobacco Hornworm. And don't miss the case full of flat wood chips that suddenly move en masse -- because they're giant cockroaches from South America.

Scuttling back past the human skeletons, kids can reflect on the cockroach's 300 million-year history and modern man's relatively brief sojourn on the planet. Back at the Rotunda Gallery, move clockwise toward Earth, Moon and Meteorites. At the entrance there's a huge rotating globe showing a color-coded geologist's view of the world, atop a base of polished rock samples. Inside the hall there are touchable stalagmites, meteors and odd-shaped natural concretions, including a "Dumbbell" from South Dakota. And in the Moon Hall on a wall behind a display of five moon rocks (nontouchable, since they're encased in plexiglass pyramids), there's a small diorama of Astronaut Harrison Schmitt walking on the moon and a tape of the excited voices of Schmitt and Eugene Cernan as they talk with Robert Parker back at Mission Control.

Go straight, then turn right past a sea of jade, raw, polished and intricately carved, to the Gem Hall. There's always a line-up to see the famed 45.5-carat Hope Diamond (on the far left wall), largest blue diamond in the world. But just as fascinating are all the lesser stones, notable not only for their size and value but also for the romantic histories attached to them: Marie Antoinette's diamond earrings -- removed before or after her trip to the guillotine? -- and Empress Marie Louise's diamond-and-turquoise tiara. And the stories and intrigues surrounding some of the jewels once owned by maharanis, sultans and emperors should provide some raw material for creative writing class.

Leaving the Gem Hall, you'll pass case after case of mineral specimens, some of which put diamonds to shame with their natural glitter and strange and improbable shapes. The Amethyst and Quartz case is a real gem.

Before you head downstairs to the museum shop and cafeteria, make a quick foray into Human Origin and Variation, bannered by a skull. Just past the genetic display is the mummy case where, along with a decomposing unwrapped Egyptian mummy and a sitting-up Peruvian desert mummy, you'll find the remains of Wilhelm von Ellenbogen. He died in Philadelphia of yellow fever in 1792, was buried and, by a quirk of nature, turned to soap. He died with his socks on. ESPECIALLY FOR KIDS

The Natural History Museum, on the Mall between Ninth and 11th streets NW, is open 10 to 5:30 daily except Christmas. For a recorded message listing hours, events and activities call 357-2700, 9 to 5. The nearest Metro stops are Smithsonian or Federal Triangle on the Orange and Blue lines. Special children's programs and services include:

DISCOVERY ROOM --

Visitors of all ages can get their hands on objects from the museum's collections here, but the target is 6- to 12-year-olds. There are shells, fossils, snakeskins, bones and preserved specimens in jars. It's free but because it's so popular and only 30 people at a time are allowed in the room, you must pick up passes at the Discovery Room door for your half-hour allotment of sifting through the specimen drawers and finding the answers to the quizzes. Monday to Thursday, you can visit noon to 2:30; Friday through Sunday it's 10:30 to 3:30. Call 357-2700.

THE INSECT ZOO --

Observe a leafcutter ant colony, a beehive and many insects, large and small but all very alive. There are experts on hand to answer questions and they'll even let you pet some of the larger specimens. A highlight is watching the tarantulas munch their dinners, weekdays at 10:30, 11:30 and 1:30; weekends and holidays at 11:30, 12:30 and 1:30. Open during museum hours.

THE NATURALIST CENTER --

For older children (12 and up) and amateur scientists, this is a working reference library with thousands of books and study collections to aid in identifying plant, animal and mineral specimens. Identi-Days, held every other month on Saturdays, are a chance for anyone to bring in a "find" and identify it with the help of experts. The Center's hours are 10:30 to 1 Monday to Saturday; noon to 5 Sunday. Call 357-2804.

SPECIAL PROGRAMS --

The museum often accompanies special exhibits with family workshops and films. For dates and times, check out the Smithsonian calendar that appears the first Friday of each month in the Weekend section or pick up a Quarterly Calendar of Events at the Information Desk (or write the Office of Education, National Museum of Natural History, No. 158, Washington DC 20560 and ask to be put on the Quarterly's mailing list).

MUSEUM SHOP --

A nice mix of inexpensive things kids can buy for souvenirs -- plastic dinosaurs, animal stickers, posters, stationery -- and pricier items that are fun and educational, including an ant farm (You Take the Farm, We Mail the Ants), dinosaur models and bird mobiles. Crafts are organized by geographical area and subject. And if you run out of money, there's a MOST cash machine at the cafeteria entrance.

CAFETERIA --

Open 10 to 5 daily, the second-favorite carousel on the Mall (after the Smithsonian merry-go-round) dispenses hamburgers, hot dogs, fries, jello and jumbo cookies via conveyor belt.