Atlanta Hawks center Tree Rollins was fined $5,000 yesterday and suspended, without pay, for the first five games of next season for precipitating a bench-clearing brawl at Boston Garden Sunday in a nationally televised NBA playoff game against the Celtics.

Celtics guard Danny Ainge, the other principal in the incident, was fined $1,000, plus $250 for being ejected from the game, which the Celtics won, 98-79, to advance to the Eastern Conference semifinals.

The incident came in the third quarter when, going upcourt after a dunk, Rollins struck Ainge in the face with his elbow and Ainge retaliated by tackling Rollins. Players from both teams then joined in a brawl.

Ainge and Atlanta's Mike Glenn were the only players ejected.

In the ensuing free-for-all, videotapes show that Rollins bit the middle finger on Ainge's right (shooting hand) so deeply that it required five stitches and Ainge is doubtful for Wednesday night's opening game of the series against Milwaukee.

The penalty given Rollins is the second-most severe in NBA history.

Kermit Washington of the Los Angeles Lakers was fined $10,000 and suspended for 60 days for punching Houston's Rudy Tomjanovich in a game at the Forum, Dec. 9, 1977.

Scotty Stirling, the NBA's vice president for operations, said the investigation will continue "into the role played by others," but added that Rollins was the main culprit.

"This was without question a vicious elbow thrown by a player who has a history of elbowing violations," said Stirling. "Although it clearly was Rollins who precipitated the incident, provocation is no justification for Ainge's actions. By tackling Rollins, Ainge escalated the incident to dangerous proportions."

Mike Gearon, president of the Hawks, disputed the contention that Rollins instigated the brawl. "I have visual evidence clear as a bell that Ainge initiated the contact," he said. "What happened was Ainge telegraphed his punch and Tree beat him to it. We'll request a hearing."

Rollins was fined three times for elbowing in the 1981-82 seasons.

"Fighting has no place in the sport of basketball," said NBA Commissioner Larry O'Brien, "and it simply won't be tolerated. Our resolve in this area was explained to players, coaches and general managers prior to the start of the playoffs."

In the playoffs: EASTERN CONFERENCE

Bucks-Celtics

If the Bucks could ever stay healthy, they would be a threat to win everything. They've had a week to rest, but that wasn't enough for Dave Cowens to get ready.

Cowens, who played in only 40 regular season games, has a strained tendon in his right knee and will miss at least the first four games of the series.

Sidney Moncrief (22.5 points a game) and Marques Johnson (21.4) are the keys both offensively and defensively, and with Brian Winters and Junior Bridgeman healthy, the Bucks have the best outside shooting team left in the playoffs. The question is: can they rebound with the Celtics? Without Cowens and with Bob Lanier on creaky knees, it's doubtful.

The two teams went 3-3 against each other during the regular season. WESTERN CONFERENCE

Spurs-Nuggets

Many experts feel the Spurs are good enough to unseat the Los Angeles Lakers. They'll have to get by Denver first.

The Nuggets upset Phoenix in the first round, becoming only the sixth team since the miniseries were adopted in 1975 to advance after losing Game 1. That best-of-seven conference semifinal series begins tonight in San Antonio (ESPN cable at 8).

This should be a high-scoring series, with two of the top three offensive teams in the NBA, and three of the top four individual scorers, Alex English and Kiki Vandeweghe of Denver and George Gervin of San Antonio.

English, the league's top scorer, had 42 points in the deciding third game of the first-round series with Phoenix.

Gervin was fourth in the NBA in scoring at 26.2, his lowest total in six years.