VISITING the world's most popular museum with children in tow can be a little daunting. But there are some pretty propelling reasons why 10 million visitors on average touch down at the National Air and Space Museum each year.

For most kids, the attraction is getting a close-up look at the hardware: out-of-this-world Lunar Landers, space capsules, fighter planes. Where else can you touch a piece of the moon? And what other museum has a branch on Mars?

Far out, but true. En route to Mars, a Viking I Lander beamed a signal back to earth July 1, 1976, activating a laser that cut the ribbon to officially open NASM. Now sitting on Mars, the Viking Lander has been deeded to the museum by NASA. "It's part of our collection, a mini-branch of the museum," says Rita Cipalla, chief of the museum's public affairs and museum services department. "If you get up there, take a look."

Cipalla says part of the museum's kid appeal also lies in its immediacy. "Just about everything in the museum has happened within a grandparent's lifetime -- and some of the events have happened within a kid's own lifetime." And although air travel isn't as novel to today's children as it was during their parents' childhood, parents can generate interest in the history of flight by showing their offspring just how far we've come in one long lifetime.

"A good approach to spark interest is to compare aircraft sizes, materials, fuel source, capacity, duration of flight and how they land," says Cipalla. For example, standing in the Milestones of Flight gallery, you can look up at the first successful airplane, the Wright flyer that traveled exactly 120 feet in 12 seconds back in 1903, and then glance over at the Apollo 11 capsule that rocketed three men approximately 238,000 miles to the moon in three days in 1969.

Kasse Andrews-Weller, director of education for the museum, says the most-asked questions by young visitors are predictably nitty gritty, namely: How do astronauts eat, sleep and go to the bathroom?

Herewith, three orbits you can trace around NASM's galaxy of galleries to find the answers to these questions and more. Each tour is geared to a different age group -- pre-school, five to eight and nine to 12 -- and each tour is selective, with an eye on kids' museum-tolerance clocks. You and yours could wander for days, dazed, if you tried to see it all. But you live here; you can come back again next weekend. Each tour begins at the Mall-side museum entrance in the glass hangar called the Milestones of Flight gallery.

PRE-SCHOOLERS

Late winter, when the tourist crowds are at their lowest ebb, is the ideal time to hit the museum with little ones. Arriving shortly after the 10 a.m. opening is a good idea, too. And this January, NASM published a colorful, chatty guide for young visitors, which is available free at the information desk. The guide lists 11 stops, about the limit of a young visitor's concentration span, and it makes a great souvenir.

Store coats, boots and other cold weather paraphernalia in the free cloak room on the left. (You can take a stroller around the museum but it'll be a nuisance; strollers aren't allowed on the escalators, so you'll have to line up for the elevators located in the middle of the museum.)

Start at the moon rock (properly labeled Lunar Sample), a small, flat piece of 4 billion-year-old dark gray basalt. It may not impress the very young much. Direct their gaze instead to 12 o'clock high, where the wood-and-cloth Wright Flyer, the flying machine that started it all, skims along with a dashing begoggled pilot lying flat on his stomach. Why is he on his stomach? Because that's how he steered, with his hips resting in a cradle attached to the plane's rudder. The plane's historic first flight in 1903 lasted only 12 seconds, and the plane didn't fly any higher than it now hangs in the museum.

At 6 o'clock low rests the Apollo 11 Command Module Columbia that took three men to the vicinity of the moon in 1969 (yes, that long ago). You can peer into the small (10-foot, 7-inch high) capsule and see one upside-down white-suited astronaut jammed in like just one more microchip. The other two astronauts are probably on the moon in their Lunar Lander. The printed guide exhorts kids to think about how excited the astronauts must have been, but you might ask them whether they'd relish eight days in these close quarters. (And, yes, how would you go to the bathroom?)

Moving right along -- little kids last longer in a museum if you change your venue often -- take the up escalator, to the left if you're facing the moon rock. Kids will like putting their feet in the feet of the man who painted the footprints on the escalator. At the top, head straight ahead past Skylab (not recommended for little ones since the line is often long) on your left, and bathrooms and water fountains (there are low ones for people with short legs) on the right, to Gallery 211, Flight and the Arts.

A sharp left inside this gallery brings you face to face with the truly phantasmagorical S.S. Pussiewillow II, artist Rowland Emmett's futuristic flying machine. As airy baroque music renders the atmosphere celestial, this amazing amalgam of household objects -- bicycle wheels, badminton birdies, clothesline pulleys, floral carpets, chandeliers -- gently tilts, spins and flaps. It's spellbinding, especially for tots. On board are the wiry pilot, Dr. Leo Capricorn, and his similarly fashioned-of-wire Astrocat, roasting chocolate-chip cookies on a toasting fork. The prominently displayed "Artist's Account of His Machine" invites "Beings from Other Places to come aboard for tea and toasted tea cakes." Unfortunately, the wonderfully weird contraption is behind plexiglass, preventing kids from taking the artist up on his invitation. (And even more unfortunately, this gallery is closed for renovations until the end of April.)

Leave the gallery and turn left, stopping to get a meteorite's view of the Milestones of Flight gallery through the glass balustrade on the right, on your way to Gallery 206, Balloons and Airships. On the left as you enter is a tableau depicting a life-size Benjamin Franklin watching the first manned balloon flight from his Paris balcony. A suitably French- accented voice tells the story of the history-making flight. And floating straight ahead are two large models of the Montgolfier Brothers' famous hot air balloons, a brilliant royal blue one festooned with golden eagles and lion heads and a bright red-and-white striped one with a red velvet "sleigh" in which the first two men to fly in a gas balloon wafted aloft over Paris in 1783. To the right of these is a large yellow balloon rhythmically rising and falling as it fills with hot air, a simple lesson in hot air rising. On a sunny day, you can see the hot air's rippling shadow on the wall behind the balloon.

Make a right turn into the Puppet Theater and catch the continuously running show about the first balloon crossing of the English Channel in 1785. Settle onto low stools and watch the tongue-in-cheek show which combines illuminated panels, puppets and simulated action to get across the principle of traveling light. Just about everything -- including the pilots' clothes -- is jettisoned to maintain altitude. The show is short -- only five minutes -- and funny, although the taped soundtrack is somewhat muffled.

Leaving the puppet theater, turn right to see the Double Eagle II, the first balloon to cross the Atlantic (in 1978). You'll see only a fragment of the balloon envelope but this is the actual gondola, which looks like a boat out of water. The three pilots are here -- or at least life masks of their faces attached to dummies dressed in the clothes they wore on their history-making flight. Nearby is a video monitor showing highlights of the flight including the exciting impromptu landing in a field in France -- reminiscent of the puppet show's everything-overboard landing almost 200 years earlier. (Some things do stay the same.)

Turn right into the main hall and straight ahead are a couple of "face" planes hanging from the ceiling. There's a fierce-looking 1938 Curtiss 40E Warhawk with a scowling eye and shark-like teeth painted on the plane's nose. Nearby is a snubnosed Boeing P-26A called a Peashooter. It's a short and stubby pre-WWII plane that looks like a Pekinese pup complete with painted paws. Ask your kids what they think the planes look like.

Then take the stairs to your right, down into Gallery 102, the Hall of Air Transportation, and turn left toward the disembodied nose section of American Airlines' Vermont, a DC-7 that saw service in the '50s. Climb the steps to the cockpit to get a close-up view of the control panel's dials, knobs, buttons and switches. The aisles in this obsolete plane are just as narrow as today's but the seats are wide and comfy , there's glossy wood panelling everywhere and patterned curtains at the windows, and the streamlined lavatory looks far more spacious and up-to-date than today's modern conveniences.

Back in the main hall, you'll find yourself facing the museum's huge gift shop filled with books, models, kites and souvenirs (with a MOST cash machine conveniently posted outside) to your left, and restrooms and a baby station on your right. So, count your change or change your baby. FIVE- TO EIGHT-YEAR-OLDS

You can usually catch the interest of this age group with action stories, and NASM has volumes of them. Using the moon rock as your starting point, aim your eyes 2 o'clock high at the Spirit of St. Louis in which Wunderkind aviator Charles Lindbergh made the first solo flight across the Atlantic in 1927. He was only 25 years old, and he made the flight in 33 hours without aid of radio or parachute, and with only ham sandwiches to sustain him. He also won $25,000 for his feat.

Just to the right at 3 o'clock low is the Mercury Friendship 7, the remarkably small (only 6 feet wide) capsule in which another flight pioneer, John H. Glenn Jr., became the first American to orbit the earth, in 1962. Inside the capsule you can see a silver-suited Glenn dummy wedged into the capsule like a sardine in a can. Not very comfortable, but the view was fabulous: Glenn saw four sunsets in five hours from his orbital perch.

Walk straight ahead toward the Independence Avenue entrance. Tilting perilously low over the information desk is NASM's newest acquisition, the blue and white Voyager, the "flying fueltank" that made the first unrefueled, non-stop flight around the world in December 1986. The wingspan is truly awesome -- 110 feet, 8 inches. The plane had to be tilted to fit in the space and you can almost reach up and touch it. Information about the flight abounds, in easy-to-read panels and on video monitors showing news clips. (Hey, this must be real. It was on TV!) Here's a good opportunity to give kids some perspective on technology's rapid march by comparing the first flight around the world -- by a Douglas World Cruiser, which took six months and many refueling stops back in 1924 -- with Voyager's nine days, three minutes and 44 seconds.

Head up the escalator to the left of the information desk and turn right at the top to Gallery 208, Pioneers of Flight. This carpeted, quiet, usually uncrowded gallery is a great place to plop down and tell some in-depth stories about the planes exhibited here. In the center of the gallery is Amelia Earhart's lipstick-red Lockheed Vega 5B in which she made the first solo flight across the Atlantic by a woman, in 1932. Earhart's other record-setting flights and mysterious disappearance during an around-the-world flight attempt in 1937 make for exciting storytelling.

Above and behind Earhart's plane is another, less famous today but a whopper of a legend in its own time. The Vin Fizz is a 1911 vintage Wright Model X with bunches of grapes painted on the underwings alongside the slogan "The Ideal Grape Drink." The commercial virtues of flying machines had been quickly recognized and this plane, sponsored by a soft drink company, set off to cross the United States and capture the $50,000 prize offered by William Randolph Hearst to the first pilot to complete the flight in less than 30 days.

Well, pilot Calbraith Perry Rodgers made it -- but too late to win the prize. It took him 80 flying hours over 49 days, 70 landings and 16 accidents. Along the way his plane was rebuilt several times using spare parts carried in a railroad car that followed the plane's route. The story is a great tribute to perseverance and good old American hoopla. Take a look at the posters the Vin Fizz company printed detailing the chronology of Rodgers' accidents that ranged from "Struck tree, fell 75 feet, Rodgers slightly hurt" to "Complete wreck, fell 200 feet, Rodgers badly hurt."

From Pioneers of Flight, turn left and walk to the west end of the hall where, at the top of the stairs, you'll find a 1:100 scale model of the USS Enterprise, the first nuclear-powered aircraft carrier, built in 1960. This is a model builder's dream, or nightmare: Stephen Henninger worked more than 12,000 hours over 12 years to complete the model, with squadrons of folded-wing planes, helicopters, trucks and assorted other vehicles parked on deck.

About turn, right march and you can board the simulated deck of an aircraft carrier in Gallery 203, Sea-Air Operations. As Navy etiquette requires for VIPs, you're piped aboard the hangar deck where a real folded-wing Grumman F4F Wildcat (also known as the FM-1) squats. This entire gallery is awash in battleship gray, right down to the regulation trash cans. In the pursuit of authenticity, there's even a porthole with a view of filmed ships at sea. Stare through the porthole long enough and you really will feel at sea.

Standing near the porthole is the Indiana Jones-like figure of an aircraft carrier Plane Captain with massive tiedown chains wrapped around his neck. His job is to service, inspect and get planes ready to fly. He cuts quite a dashing figure and should inspire some youngsters to think of future enlistment.

Climb the gray stairs to the bridge and watch filmed planes taking off from a real carrier and take a turn at the tiny wheel by which great ships are steered these days. Climb down another set of stairs past ominous, bright yellow Abandon Ship lockers to the Ready Room, where a fighter squadron briefing is always in progress, featuring a film on aircraft carriers and a "Top Gun" view of air combat from the cockpit of an F14 Tomcat. The show lasts about five minutes.

Disembark and take the stairs just outside the gallery down to explore the Hall of Transportation's aircraft, including a spiffy silver Eastern Airlines DC-3 from the early '50s with the proud "Great Silver Fleet" logo emblazoned on the fuselage. You can almost catch a whiff of the romance that once surrounded commercial flight. And don't miss snooping around the nose section of the '50s DC-7 at the back of the hall.

From here, you can make the Museum Shop your last stop. NINE- TO 12-YEAR-OLDS

Kids this age can read just about anything, so they can pretty much guide themselves. But it helps to aim them in some promising directions. Starting at the moon rock, look to 4 o'clock high at Glamorous Glennis, the orange streamlined Bell X-1 in which Capt. Charles E. "Chuck" Yeager showed the right stuff by breaking the sound barrier back in 1947 when he was 24. The plane's named after his wife, which information you'll find posted on one of the brass stele that crop up all around this gallery. If you want information about what's overhead, look to these columns.

There's lots to explore here on the ground, and it's easy to miss some of the higher-flying craft. For instance, high above the Wright Flyer is the small silver ball with four antennae that indirectly launched America's space age and revolutionized the public schools' science curriculum. Sputnik (not the original, of course, but a replica on loan from the USSR Academy of Sciences) was the first manmade object placed into orbit around the earth. Just to its right is a replica of Pioneer 10, a U.S. satellite dish wrapped in what looks like orange and yellow foil. Launched in 1972, it's still up in space, and scheduled to pass Pluto in 1990 before spinning clear out of the solar system. What makes it extra exciting is that Pioneer carries a plaque designed to tell intelligent extraterrestrials about its mission, its point of origin and the people who built it.

Down on the ground, crouched under the Spirit of St. Louis, is the crab-like Mutch Memorial Station, a replica of the Viking I Lander up on Mars that belongs to the museum. Beside it is a plaque with a written injunction from NASA for some future astronaut -- "Maybe me, Mom?" -- to take the plaque up to Mars and permanently install it.

If you can drag your charges out of Milestones of Flight, take the escalator up and make a sharp left into the Skylab Orbital Workshop. Next to the IMAX films, this is one of the most popular and crowded exhibits at NASM, but if you arrive early, you may avoid a long wait in line. The wait is long because the viewing space is both limited and linger-inducing. This fascinating space was home and office to three astronauts for several months in space in 1973. You'll see lots of high-tech circuitry and a lot of ingenious "homey" touches, like the astronaut dummy anchored to an "individual food-serving tray," a familiar-looking articulated shaving mirror in the "bathroom" and less familiar "Waste Collection Facilities," an upright sleeping dummy in a "sleep restraint" device and a collapsible shower stall in which a decorously modest photo of an astronaut is showering. Near the shower you'll find a perfect example of NASA-speak in the posted How To Take a Shower instructions. The third step is: "Take shower. Dry interior before egressing." (Maybe a little NASA-speak would improve conditions in your child's bathroom.)

From Skylab head west to Gallery 210, Apollo to the Moon. If you have younger children tagging along with older siblings, drop the smaller ones at the entrance to this gallery in front of the "Man in the Moon Remembers," a video program with an animated man in the moon jocularly telling how he came to be. It's in an alcove where kids can safely hunker down on the carpet while older children gaze into this gallery's dioramas of lunar landings (which are under renovation until the first week in March) and huge glass wall cases full of space gear. Here's where the bathroom question is finally answered, with a clinical display of a Waste Disposal Kit. There's also an Oral Hygiene Kit, a One-Man Meal, a medical kit and other survival equipment including a bright yellow bag of shark repellent to deal with the dangers of splashdown.

In the middle of the gallery is a theater where you can rest your legs and sit down to watch a multimedia presentation titled "25 Years of Space Exploration." It's intriguing, if a little dated and sadly ironic, ending as it does with laudatory narration about the Space Shuttle as the modern symbol of America's presence in space.

Exit -- or egress -- the gallery and head downstairs to Gallery 103, Vertical Flight. Kids will automatically recognize this as "M*A*S*H" and "Platoon" territory. They can peer into the bare-bones interior of a 1954-model Sikorsky Seahorse, hundreds of which hovered over Vietnam. And they may get a kick out of some improbable WWII one-man helicopter prototypes that never got off the ground. At the back of the gallery shines the bright yellow Spirit of Texas, which in 1982 was the first helicopter to whirl around the world -- in 30 days. There's also TV film of an exciting emergency landing at sea aboard the container ship SS President McKinley after the Soviets refused to allow the helicopter a refueling stop.

The Museum Shop is on your way out. Don't forget to pick up a foil pack of freeze-dried astronaut ice cream to eat out on the Mall.

GETTING THE MOST OUT OF NASM

The National Air and Space Museum, Independence Avenue between Fourth and Seventh streets SW, is accessible both from Independence Avenue and Jefferson Drive on the Mall side. The nearest Metro is L'Enfant Plaza, or if you don't mind a little walk, the Smithsonian station is nearby. The museum has a cafeteria on the third floor, which is accessible only by elevator. It offers fast food, 10 to 5 daily. (This fall, a new glass-walled combined cafeteria and dining room seating 980 is scheduled to open.) Among the many programs for families are:

LANGLEY THEATER --

Five films about flight and space play daily in repertory on the five-story IMAX screen. It's a good idea to head straight for the ticket booth when you arrive and pick up your tickets for the show you want to see. Admission is $2 adults, $1 students and seniors. Double features of feature films are also shown in the evenings after museum hours. For schedule, call 357-1686.

ALBERT EINSTEIN PLANETARIUM --

There's a show every 40 minutes except on Tuesdays and Thursdays when the three midday shows are replaced by "Noontime With the Stars" lectures. The show is recommended for ages 10 and up and the lectures for older children. Admission to the planetarium is $2 adults, $1 children, students and senior citizens. The lectures are free.

PAUL E. GARBER FACILITY --

NASM's Suitland warehouse and restoration shop -- with 140 air and spacecraft on view in five buildings is open for tours on a reservations-only basis by calling 357-1400. But the weekend of April 23-24, everyone's invited to a weekend-long free open house for demonstrations and tours. Call 357-2700.

FAMILY NIGHTS --

Some nights during the summer, NASM offers special hands-on programs for families. For information, call 357-2700.

HANDICAPPED SERVICES --

NASM offers special services and tours for disabled, visually- and hearing-impaired and mentally retarded visitors. Call 357-1400 for information.

MONTHLY CALENDAR --

For a free monthly events calendar, including free film and lectures series, write Calendar, Room 3363, National Air and Space Museum, Washington DC 20560.

I read somewhere that words with the letter K in them are funnier than words without it. Want to see if it's true? Perform a scientific experiment: Ask the child of your choice to read the following place names out loud without laughing.

1. Kaffeeklubben

2. Kalamazoo

3. Kankakee

4. Karnataka

5. Kidderminster

6. Killiecrankie

7. Klagenfurt

8. Kokomo

9. Krugersdorp

10. Kuria Muria