Guillermo Vilas won the $175,000 Washington Star International tennis tournament yesterday when Victor Pecci collapsed, overcome by leg cramps, as the two played a second set tie breaker.

Vilas was leading, 7-6, 6-6 and up by 4-3 in the tie breaker, when Pecci served. Pecci punched a volley long, turned and went down. He tried once to get up, then fell flat on his back, writhing in agony.

Vilas came around the net to his aid and was joined by tour trainer Bill Norris. As J. D. Strong announced that Pecci had forfeited the match because of "loss of physical condition."

Pecci, who had fallen twice earlier, was given less time to recover from the cramps than some players were given to argue with umpires during the week. He remained lying on the court surrounded by cameramen and ball boys for about 15 minutes as Norris applied wet towels.

He was helped from the court, but 30 minutes later was up and walking around, saying he planned to play his first-round match Tuesday in Louisville.

Once he fell, Pecci had 90 seconds to resume play - 30 seconds to serve again, another 30 seconds before he was penalized a point, then 30 seconds more before he was penalized a game. The game penalty gave Vilas the match, 7-6, 7-6.

Ironically, tournament officials had planned to start the final at 7 p.m. to avoid afternoon heat. Friday, they changed the starting time to 2 p.m. to accommodate PBS television, which did not want to tape the match, because of technical difficulties, so close to its scheduled airing at 10 p.m.

The ending left many in the crowd of 5,800 stunned and a number of them booed when Strong announced the default without further explanation.

Pecci did not complain, however.

"The rules are the rules," he said.

The bizarre finish married a brilliant match. Vilas, 26, the Argentinian who won this title in 1975 and 1977, and Pecci, 23, the Paraguayan who may be the most improved player in the world this year, battled 95-degree heat and each other for 2 hours 24 minutes in a match that was virtually even when terminated. Villas won $24,500 and Pecci received $12,250 as runner-up.

Vilas was at his best in the crunch. In the first set, down 5-4, 30-0, he became the Vilas of 1977, the world's dominat player. First he passed Pecci with a backhand, then hit a forehand for a clear winner.

Pecci responded with an overhead to reach set point but Vilas landed a lob right on the baseline to get to deuce. Pecci got his next two serves in and charged the net only to watch Vilas forehands whistle past.

"He passed well," Pecci said through his interpreter and coach, Tito Vazquez. "He surprised me that he hit those shots so well. His ground strokes today were very good."

Pecci's ground strokes, almost flawless all week, were inconsitent. He made a number of unforced errors and eventually began coming to net almost every chance he had.

"My backhand was not good today," he said. "I came to t e net partly because of that and partly because I was tired and wanted shorter points."

Vilas was superb in the first set tie breaker. All week long he had been telling skeptics that he was playing well, and when he had to yesterday he proved it.

Pecci got to 2-2 in the tie breaker with a winning volley, then Vilas took charge. He slammed a forehand winner past the charging Pecci for a 3-2 lead, and got to 4-2 on a similar shot with his backhand. Pecci's service winner made it 4-3 but Villas came right back with two more backhand passing shots for 6-3.

On set point he was just wide with a backhand but hit another backhand that nipped t e tape as it flashed across court and by the diving Pecci.

"At times this week I played as well as I did in 1977," Vilas said. "Today I was good and so was he. I'm sorry the match ended the way it did. You don't like to win that way, but conditioning is part of the game."

Norris said that during the second set he began to worry that t e heat was troubling Pecci. Pecci said he first felt the cramps coming on at 3-3 in that set when he stretched to reach a shot.

"I felt something and I was worried," he said. "I was hoping to try not to run and get through it."

With Vilas serving at 5-6 and leading, 40-30, the two played a classic point. First they took turns lobbing deep until Pecci suddenly charged the net and hit what looked like a drop-volley winner.

Vilas somehow reached the ball and seemed to have the ball past Pecci, who just reached it and lobbed back. Vilas hit an overhead and Pecci just got the ball back to Vilas, who finanlly put the point away in the corner.

The tie breaker reached 4-3 with Pecci serving. He leaned into a first serve and followed it to net. Vilas punched the ball back down the middle and Pecci, trying to be too perfect, volleyed long.

Then, as he turned from the net, he collapsed.

"I was very hot and tired," he said. "I just felt pain in my leg and went down."

Pecci would have needed at least 30 minutes to recover. Since the umpire ruled that he had suffered a "loss of physical condition" and not an injury, he had 90 seconds to put the ball in play. Had he been injured - no one could explain why a cramp is not considered an injury - he would have been allowed five minutes. Pecci said it was the first time he had had cramps.

"This is a sad way to win," Vilas said. "I felt in the second set he was tired. He looked that way. He was trying to overhit his shots from the baseline and on some points he was resting."

Vilas would not commit himself to defending his title next year and as he left to catch a plane said, "I think they should get the mayor to put air-conditioning in for all Washington, including here."

Pecci, who beat Vilas in the quarterfinals of the French Open, the only time in eight meetings he has beaten him, said he was pleased with his overall play here.

"I had a good week," he said. "It is too bad it ended the way it did."

In Spanish or English, no one summed up the finale any better. CAPTION: Pictures 1 and 2, Victor Pecci writhes in pain (top) before trainer Bill Norris and Guillermo Vilas (bottom) can come to his aid. Photos by Richard Darcey - The Washington Post; Picture 3, Guillermo Vilas lashes a forehand at Victor Pecci. By Richard Darcey - The Washington Post