The first Saturday of the French Open Tennis Championships was crowded . . . with people, with color and with the simmering excitement of intriguing matches.

Monday is Pentecost, a state holiday in predominantly Catholic France, and so the crowd of more than 17,000 spectators that jammed every nook and cranny of Stade Roland Garros was in a festive mood for the start of the long weekend.

Their fashions, the splashiest and most revealing the great French designers have to offer, brightened a gray, oppressively muggy day. So did the overall quality of the tennis. The program one looked, there seemed to be something interesting happening on the red clay courts.

Chris Evert ran into unexpected trouble, losing six games in a row from 4-0 up in the first set before overcoming stubborn Ivanna Madruga, 4-6, 6-2, 6-3.

Harold Solomon got blasted off the court for two sets, recovered, then had to fight off two match points to beat Stan Smith, 3-6, 1-6, 6-3, 6-1, 8-6.

Gene Mayer, who defaulted in the semifinals of the Italian Open last weekend after suffering cramps, won his second consecutive match from two sets down, this time recovering from 1-3 in the fourth set to beat Brian Gottfried, 1-6, 6-7, 7-6, 6-3, 6-2.

Even matches that were not so desperately close had their moments.

Wojtek Fibak of Poland arrived late for his center-court match against Frenchman Dominique Bedel, and was almost defaulted, because he was watching the Pope's visit to his homeland on television.

Once he got on court, Fibak had an evenful afternoon. He blew a big lead in the first set, came back from 2-5 down in the second, and then had to withstand the ire of the crowd as well as the steady but inexperienced Bedel to squeeze out a 5-7, 7-6, 7-5, 6-2 victory.

The crowd's enmity resulted from a dispute in the second-set tie breaker, in which Bedel missed a passing shot, then asked to have the point replayed because there had been so much commotion in the crowd during the point. Fibak objected, rightfully, but the crowd was on him thereafter.

The stadium crowd was just as engrossed and enchanted by Jimmy Connor' rugged but sporting 7-6, 6-2, 7-5 victory over Australian Ross Case at nightfall.

This was as hard-fought as any straight-sets match could be. The knowledgeable Parisian spectators were enthralled by the aggressive all court points, and by Connors' uniquely brutish, animalistic style - a physical type of tennis the likes of which they have seldom seen before, all grunting and flying through the air.

But they admired and applauded Case's battling spirit as well. He does not have Connor's talent or wealth of shot, but he scampered all over the court, diving for shots, working his way in to press Connors from the net.

By the end of the second set, both players were sopping wet, their hair matted. Case's knees were scraped raw, blood streamed down his right leg from a nasty abrasion, and his shorts were splotched with clay - red badges of courage left from his numerous sprawls at shots he couldn't quite reach.

In the third set, Case tired badly, but kept counterpunching like a fighter trying to make it through the 15th round. When he suffered leg cramps at the end of the seventh game Connors climbed over the net, put his arm around Case's shoulders, and walked him to his chair for the changeover.

It was that kind of a match - intense but friendly, recalling days when tennis players were not as hardhearted and badly hebaved as so many are today - and the crowd loved it, as much for its spirit as its sometimes inspired shotmaking.

There was bravado, esprit and good tennis, too, as four Americans occupied court No. 2 - tucked away in a corner of the scenic grounds, underneath the stadium, surrounded by only about 1,000 seats - for seven hours.

Gottfried - who is just starting to regain his form after taking six weeks off to celebrate the birth of his first child, hardly missed a ball in the first two sets, and saved three set points from 3-6 down in the second-set tie breaker against Mayer.

But then he tired and started missing his first serve, blew a couple of weary overheads and Mayer came on strongly, Mayer hits both forehand and backhand with a two-fisted grip, and he mixed up his game cleverly in the last three sets, coming to the net when he had openings, out-dueling Gottfried from the backcourt when those tactics were called for.

The match which followed this four-hour thriller was even more exciting - unexpectedly, since Solomon had not lost to Smith in eight years, and had seldom been troubled by him on a clay court.

But for two sets, Smith served exceptionally well, ran around and pounded big forehand returns of Solomon second serves, and played hardhitting, gambling tennis. He was aided by an uncharacteristic number of errors off Solomon's racket.

It seemed as if it would be over quickly, but suddenly Solomon, in his words, "got stuck into it." Smith's legs tired as Gottfried's had, he stopped moving after stroking the ball and his first serve deserted him. The backhand dropshorts that had been so effective in bringing Solomon into vulnerable position at the net started missing.

Solomon won the third and fourth sets easily, but just as Smith seemed about to expire, he regained the patient attitude with an undercurrent of aggression that had worked so well earlier. He moved Solomon around, got in for some big volleys, and seemed capable of winning after hauling himself back from 3-3, 0-40, in the final set with four big serves after Solomon had floated a backhand return long.

Smith had two match points in the 10th game, Solomon serving at 4-5.

Solomon survived two match points and Smith finished himself off by double-faulting and then netting a forehand on the final two points. He left the court distraught. He had played well, on balance, but he no longer seems to know how to win.

An anti-apartheid group demonstrated on the grounds of the stadium and other protestors chained themselves inside the office of the tournament director. They were protesting the participation of seven South African players. CAPTION: Picure, Harold Solomon was forced to stave off two match points before defeating Stan Smith in French Open, 3-6, 1-6, 6-3, 6-1, 8-6. AP