FIVE THOUSAND persons, more or less, spent Saturday afternoon facing downwind on the Washington Monument grounds, each holding as arm aloft.

It was as though all the children, women and men in a small town had turned out for ballet practice, and it made a charming scene. Which was the whole and entire purpose of the third annual kite festival, according to organizer John Carrington. There was no competition and no prizes and no rules, nobody was in charge, and please walk on the grass.

The National Park Service gave away 2,000 paper kites and disappointed at least as many more clamoring children when the supply ran out around 2 p.m. Many of the kids were trying for seconds, because the rate of attrition was norrendous, what with the gusty wind and the kite-eatiang trees that dot and border the Mall.

Most of the adults had brought kites of their own, so that at times there were perhaps 3,000 aloft together, sailing, dodging, weaving, diving; more kites than there was sky available. Thus it was necessary to interact with one's neighbors. Two enterprisings young men managed to get their kite strings entangled with those of two young women, and some nimble footwork expanded the tangle to the young women themselves. Shortly afterward they gave the kites to some children and strolled off uptown, arm in arm in arm in arm.

By sundown the grass was one great web of string, and the trees from the Loncoln Memorial to the Ellipse were festooned with fragments that must have gladdened the heart of visiting Prime Minister Fukuda of Japan, where they know about kites.

The people at the Monument didn't know kites, according t John Barr of Bethesda, who reeled in his homemade compound box kite for good after being fouled for the umpteenth time by what he called "amateurs."

Barr had come to look over the terrain and situation in preparation for this Saturdays' Smithsonian competition (homemade kites only, register by noon on the Monument grounds), sponsored and directed by the institution's legendary Paul Garber.

Garber, 77, was almost drowned at the age of five when a kite dragged him into the ocean, according to Kitelines Magazine , the quaterly journal (yes!) of the American kitefliers Association. Garber, a native Washingtonian, shook of that scare and went on to survive flights in a glider he built after being inspired by watching the Wright Brothers and the doomed Lt. Selfridge fly the Wright power kite at Fort Myer.

Garber hung around the Smith sonian so much they finally put him to work in what now is the air and space division; he stayed there 56 years before retiring, then came back to work fulltime as Historian Emeritus. Garber invented the target kites that trained Navy antiaircraft gunners in World War 11. (Civil Defense zealots also used the kites, which were painted to represent Zeros and Messerschmitts, to test whether volunteer skywatchers in Cooperstown and Keokuk had done their enemy aircraft identification homework.)

Garber once had his kite bridle adjusted by and was patted on the head by Alexander Graham Bell, whose fascination with kites led to the invention of the superstable man-carrying tetrahedral kite and seriously interfered with the development of the telephone.

Garber has been collecting kites like a shoplifter all his life, although he hasn't yet gotten once into the new Air and Space Museum. He started the Smithsonian Kite Carnival on a whim (Smithsonian Secretary S. Dillon Ripley's whim) in 1967, and every year presides fromt the reviewing platform like Walter Cronkite on a day when there's been nothing but good news.

"Be some heavy kites here Saturday," Barr said. "These people" - he dismissed the happy multitude with an offhand wave - "they think you spend 39 cents at the drugstore and you've got a kite . That stuff is trash. If you're going to fly kites you have to get serious, study the aerodynamics of it and construction materials and techniques."

That ain't necessarily so, according to Chuck Bernstein, owner of the Kite Site at 1075 Winconsin Ave. NW. "Almost any kite that will fly is fun, and the fun is the important thing," he said. "But the more advanced the kite is the more fun you'll have."

Berstein sells some pretty advanced kites, such as the Ghost Clipper, a $35 assembly which, if you succeed is aslsembling it, looks like the Cutty Sark under full said, bound for that great Home Port in the sky. You can spend more, but also less - Bernstein always keeps an ample stock of relatively inexpensive kits for kids.

"Americans tend to think of kites as frivolous, something kids fool with," Bernstein said. "Actually, kite building is an ancient art, and in Asia, particularly, whole cities get involved."

According to Kitelines , Hamamatsu, a Japanese city of 500,000 becomes a city of a million during the annual kite frenzy in the first week of May.

Fifty-man teams, each representing one of the city's 49 districts, cram together in a stadium the size of a football field and dogfight with huge kites that take acres of silk and paper and forests of bamboo to build.

And in Tokyo last Nov. 19, Tsuyoshi Odawara, Yjoshitomo Yoshimura, Shinosuke Toba, Yoshio Harada, Katsuhiko Kitano and Morihiro Okada flew, with the assistance of Takeshi Nishibayashi, a train of 1,585 kites on one line, breaking the world record by 150 kites. They had 300 more ready but the wind was bad.

In many parts of Asia kites are flown on New YearsDay above the houses of families that have had a son during the year. Malaysians fly kites to appease the wind gods. In Medieval Europe they used kites to drop firebombs into besieged cities. A 2,220-year-old kite model was found in an Egyptian tomb.

The most educated guessers credit the Chinese with the invention of the kite, which seems logical enough considering they also invented silk and paper and had plenty of bamboo. David Pelham, in The Penguin Book of Kites , says Emperor Wen Hsuan Ti of the Kao Yang Dynasty amused himself by "freeing" prisoners by sending them up a tower with bamboo mats and ordering them to fly to the ground. If they could walk away, they could walk away.

The French used observation kites in the Franco-Prussian War, but it didn't help. The U.S.Army has kites it won't talk about, and the National Aeronautics and Space Administration has kites it its proud of.

Bob Ingraham of Silver City, N.M., who would be the dean of American kite nuts if it weren't for the afore-mentioned Garber, uses kites to fish, which he says works fine except that golden eagles occasionally steal his catch before he can reel it in.