It was 4:30 in the afternoon, and on the shady plot of grass behind Courts 5 and 6 at Stade Roland Garros, a man was asleep on a yellow blanket with red and brown stripes. He had his shoes off and a navy blue windbreaker over his head to block out the light that filtered through the leafy canopy of needles and leaves formed by a grove of everygreen, maple and chestnut trees.

Beside him were a plastic bag containing among other things, a visor, suntan lotion, and a well-worn newspaper; a wicker basket with the remnants of a picnic lunch, and two bottles of beaujolais, large and empty. Obviously, this man had come fully prepared for a day of spectating at the French Open tennis championships.

Nearby, a couple strolled arm in arm and paused for a few minutes on a secluded bench before returning to watch the struggle on center court. There the crowd turned the 49-year-old cement stadium into a patchwork of lively colors and sounds on another of the sunny days that make springtime in Paris all that it is reputed to be.

Passion plays in a stadium that is dreary when empty, majestic when bursting with life, little dramas on eight side courts, tranquil hideaways in splendidly landscpaed corners of Roland Garros. These are what make this tournament a bountiful garden of delights.

"The French championships are the game's finest advertisement," Rex Bellamy, the poetic tennis correspondent of The London Times, once wrote. "The surface, clay, is grueling to play on. Yet it provides the toughest, most exacting test of all-round ability, and the most satisfying spectacle . . .

"All is grandcur and pathos. The grandeur is public - the protracted, absorbing exercises in tactics, technique, and physical and mental stamina. Except for strained sinews or attacks of cramps, the pathos is usually private - the spent, exhausted bodies, lumps of flesh on the masseur's table or the dressing room benches."

The players have enormous respect for "The French," which Arthur Ashe has called flatly "the most difficult tournament in the world to win." American audiences have come to appreciate it belatedly. NBC-TV will televise portions of the final two days this weekend, for the third year (5 p.m. Saturday and 3 p.m. Sunday on WRC-TV-4).

Many older players, and those preoccupied with getting ready for Wimbledon on grass, simply do not come here, figuring that two weeks of best-of-five-set matches on slow, red clay is a surefire way to drain energy an daccumulate frustration.

Young players, their clothing caked with salmon-colored dust, learn quickly that to win here, one must be both artist and artisn, craftsman and laborer.

The main course of th game - serve, volley, ground strokes - is served with all the trimmings in Paris: lobs, drop shots, dinks, delicate little angles. Unless a player is serving and volleying exceptionally, finesse is needed to open up the court for a point-ending shot. Tennis becomes as intellectual a game as chess or bridge, and clever, thoughtful players use every inch of the court to weave a tactical tapestry.

Mental as well as physical endurance is important because conditions can be trying. The wind swirls trickily and often blows up clouds of dust. Ball boys are frequently clumsy and fumbly, linesmen undertrained, elderly, sleepy or uninterested. When disputes arise, a language barrier can aggravate them.

"I think we have improved the officiating and ball boying it, but it is difficult," explained the charming, progressive tournament director, Pierre Darmon, himself a fine player who was runner-up here in 1963. "It is not like Wimbledon, when schools is out of session and people take their vacations to call lines. In France, these are not positions of honor and prestige. We do the best with what we have."

The French is the premier clay court championship of Europe - less raucous, impassioned, and perhaps less fun than the Italian, but more presitgious. It is the second leg of the traditional grand slam (the championships of Australia, France, Great Britain and the United States) and the only played on clay until and the U.S. Open shifted from grass in 1975.

For many Europeans who grew up on clay, it is still the tournament to win. Americans have long found Roland Garros a chamber of horrors. No American man has won the singles here since Tony Trabert in 1955.

"It's a tough tournament, lots of running, lots of hard work," said muscular Bob Lutz, who has played here five times since 1967. He lost to Frenchman Patrick Proisy in the first round this year. "When somebody mentions the French championships, I immediately think of getting cramps in the car on the way home at night, having to stop the car and walk them off.

"Americans are going to do better here because so many tournaments are on clay now. But it's still a real feat because the Europeans have been playing on this stuff all their lives. They know the clay, the heavy balls, the conditions. The footing, the flowing strokes, the watered courts are second nature to them."

Said Brain Gottfried, the last American in the men's singles this year, "I don't find it difficult to play here. Not like Italy. The people are more even-tempered.

"In Italy they go nuts. A little thing happens on the court, a bad call or something, and they get excited. They whistle. They scream. They're opinionated and they're loud. They get really involved, like they have money riding on every point.

"Here it's more reserved. They enjoy good tennis, no matter who's playing. But I love playing both places. It's a great experience."

The French have rediscovered the pleasures of their international championships. Attendance for the first nine days this year was 97,731, running nearly 20 percent ahead of last year's record two-week total of 133,208.

Enthusiasm for tennis here is the greatest it has been since the late 1920s, when "the Four Musketeers" - national heroes Jean Borotra, Rene Lacoste, Henri Cochet and Jacques Brugnon - won the Davis Cup six consecutive years (1927-1932) and monopolized the men's singles here from the time the tournament went international in 1925 through 1932.

Stade Roland Garros, named for a famous French aviator killed in action in World War I, was built to host France's first Davis Cup defense, after "Les Mousquetaires" took the cup in the U.S. in 1927. It occupies city-owned land and is operated by the French Tennis Federation.

Last weekend thousands of people were turned away because there were no tickets left to buy. More then 100 people were treated for gashes they suffered trying to scale a fence of iron spikes. Some made it inside by covering the spikes with empty soft drink cans. Gerdarmes foiled one attempt to tunnel underneath.

Cars were parked on sidewalks for blocks around Roland Garros, which is located on the western outskirts of the city, in a pleasant residential section called Auteuil. It is across the Avenue Gordon Benette from the municipal botannical gardens, just across the Avenue de la Porte D'Auteuil from the Bois de Boulogne, the Central Park of Paris. The fences and gates around the complex became hitching posts for two-wheeled vehicles of every description.

"The tennis boom is not only in the United States. It is in Europe as well," said Darmon. Added Philippe Chatrier, president of the French Tennis Federation, "After years of effort, This tournament has caught fire. It is the in things in Paris."

Unfortunately, the tennis this year had not been up to standard. There were few gripping matches on center court the first week.

Virtually all the top women are in the U.S., playing World Team Tennis, as is 1974-75 champion Bjorn Borg. Manuel Orantes, one of the most elegant clay-court specialist, is in Arlington, Va., recovering from elbow surgery.

Jimmy Connors, who has only played here twice (he lost in the first round to Harold Solomon in 1972 and to Raul Ramirez in 1973, before ascending to world No. 1 status), says he will continue to pass up Paris to prepare for Wimbledon. Roscoe Tanner and Dick Stockton did the same.

But even when the tennis is not terribly interesting, Roland Garros is a wonderful place to wander around the side courts, glimpsing at bits and pieces of matches, absorbing the flavor and the scene.

The winding walkways are lined with flowers, as are the terraces leading to the stadium - roses, geraniums, marigolds, petunias, snapdragons, pansies, a splendid floral variety in every imaginable shade.

The refreshments are similarly delightful. There are all kinds of beverages, ice cream bars flavored with Grand Marnier, crepes with sugar or apricot jam, hot dogs smothered in hot mustard and snuggled into crusty torpedo rolls that have been jabbed with a metal poker to make room for them. Or sandwiches (ham, cheese, or pate), fruit and custard pastries, delicious strawberry tarts.

There are always little tableux to savor:

Jose Higueras at a changover, gulping desperately from a big bottle of mineral water, flopping a towel over his head so that he looks like an Arab just emerged from the desert.

John McEynoe, 18, an American who had just discovered that continentals do not like their drinks especially cold, taking a bottle from a courtside cooler and grumbling to an indifferent umpire: "That's a heater, not a refrigerator."

Fiorella Bonicelli looking heaven-ward, releasing anonized soliloguy in Spanish, then explaining later: "I don't know whether it's the heat or the wind, but everybody was nervous today. And when I get nervous I say bad things."

Some grand, heartbreaking epics are witnessed only by a handful of relatives, friends, or strangers, stray cats and loudly chirping birds, and then reduced to one line on the multicolored "Tableau Des Resultants" in the main concourse, near the greentented shopping arcade.

Pam Teeguarden, who lost in the quarterfinals Tuesday after going slightly punch - at one stage she sat down and toweled off at 40-15, thinking she had won the game - will never forget a match she lost here to Kerry Melville on an outside court on a chilly, gloomy afternoon in 1972.

She served for the match several times and had a bunch of match points. But exhausted, cramping, numb in her racket hand, she could never gasp the ultimate point.

Finally she double faulted to give Melville the match, 9-7, 4-6, 16-14, then sat down beside the court and cried. After a few minutes, she dragged herself back to the dressing room to untie her knotted muscles and repair the frayed nerves that had popped through a frazzled exterior like the springs of a battered old sofa.

Melville wasn't in much better shape. When she got to the dressing room, someone told her, "You look like you lost."

"To me," Teeguardensaid, "that match will always symbolize the French championships."