Vitas Gerulaitis got a scare tonight. But it had nothing to do with his easy four-set quarterfinal victory over Bruce Manson that advanced him to a U.S. Open semifinal date Saturday against John McEnroe, also a four-set winner today.

Moments after his 6-4, 6-2, 4-6, 6-1 victory over Manson, Gerulaitis sat in the locker room talking to three reporters who had followed him in there aware of his vow not to go to the press interview room until he lost a match. His mood was relaxed, buoyant.

He already had told a USTA representative at courtside that he would not go to the interview room and would gladly take his $500 fine for refusing. As he sat and talked about the match, Gerulaitis suddenly was interrupted by his manager, Bob Kain.

"Vitas," Kain said, walking in, "you gotta go down there (to the interview room)."

"No way," Gerulaitis answered.

The two then huddled, Kain showing Gerulaitis a list of figures that indicated he had accumulated $4,600 in fines in the last 12 months. Under the rules of the Men's Professional Tennis Council, if a player accumulates more than $5,000 in fines for "minor" offenses, like skipping a postmatch interview, he is suspended for 21 days.

"The suspension starts at a date to be determined by the council," tournament referee Mike Blanchard said tonight. "But we've never suspended somebody during this tournament."

Gerulaitis, however, was unaware of that when Kain showed him the figures. He believed the suspension could be immediate.

"Well guys, I hit the big 5," he said. "I guess I gotta go, since I would like to play the semifinals."

Before Kain's entrance, Gerulaitis had at first refused to talk with anyone about his match, then relaxed. "It was a tough match for me because these are the kind I should win and haven't been," he said. "I got a little tentative in the third set, stopped coming in and let him get back. Then the fourth set I got aggressive again."

The forced ending to the Gerulaitis boycott came at the end of a day that saw McEnroe, the two-time defending champion, gasp his way to a 6-7, 7-6, 6-4, 6-2 victory over Ramesh Krishnan in a 3 hour 27 minute windblown match in which McEnroe never really got going.

At the same time, Tracy Austin, Martina Navratilova and Barbara Potter joined Chris Evert Lloyd in the women's semifinals, each with straight-set victories.

Austin survived an early scare, falling behind Sylvia Hanika of West Germany, 4-2, in the first set, but eventually wore down Hanika with her consistent, deep ground stroking to win, 6-4, 6-2. Navratilova, who has not yet faced a break point in five matches, had a crisp serve and volley duel with Anne Smith, finally prevailing, 7-5, 6-4, to move into a semifinal against old foe Evert.

Potter, reaching the semifinals here for the first time at age 19, beat a 17-year-old amateur for the second time in a row, winning, 7-5, 7-5, from Barbara Gerken.

The most competitive match of the day was McEnroe-Krishnan, played before an audience that was strangely subdued considering that McEnroe had a genuine brush with potential disaster.

McEnroe dropped the first set in a 12-10 tie breaker, uncharacteristically double-faulting on set point. "I was sluggish, I couldn't get loose out there," he said. "The wind bothered me. I don't ever remember being so tired without sweating a drop."

McEnroe's problems continued in the second set. He was disgusted, constantly berating himself for missing shots. He was angry, yelling at one fan who applauded a missed shot that his next shot would be directed at the fan. He was frustrated, muttering aloud about Krishnan having, "a 10 mile an hour serve."

Krishnan, 21, with superb touch on his ground strokes, was going for winners and, at times, making McEnroe look bad. When McEnroe double-faulted again at 4-5, 15-40, Krishnan was serving to go two sets up.

"If you had told me before the match that I would be serving to go up two sets I would have told you that you were crazy," Krishnan said. "I just told myself to keep trying."

The two players reached 30-all and then McEnroe looped yet another weak forehand. Krishnan closed in for the kill but then at the last moment decided to try a drop volley. It dropped into the net.

Now it was break point instead of set point. Krishnan saved that one but then missed two shots and McEnroe was alive at 5-5. "I let him get back in the match with that shot," Krishnan said. "It definitely gave him a lift."

It also put the two players into another tie breaker after each held serve. This time though, McEnroe came up with a big first serve at 4-4, then Krishnan hit a backhand long and just touched a volley off a McEnroe backhand.

"If I had gone down two sets it would have been tough to come back," McEnroe said. "When I got out of that second set it helped a lot. I was really struggling.

"Let's face it, nobody in the world expected me to lose this match. He just played a hell of a match."

Krishnan hung tough until 4-4 in the third when he blew a 40-0 lead and let McEnroe get the break he needed to get on top of him for good. McEnroe won that game with one of his few clean winners of the day, a whistling backhand down the line, then served out the set.