NBA Commissioner Larry O'Brien fined Boston's Dave Cowens $2,500 and Atlanta's Wayne (Tree) Rollins $1,500 yesterday for fighting during a game at the Boston Garden last Friday.

Some sources around the league had expected Cowens to be suspended as well as fined since he threw the first punch.

But the NBA report indicated that Cowens' action came in response to an elbow by Rollins that went undetected by the officials. Therefore, the NBA said, Cowens' punishment was limited to a fine.

Cowens said that Rollins "was racing down the lane and gave me an elbow. I couldn't let him get away with that."

Cowens retaliated with a punch and the two squared off. Both landed some heavy blows, but neither was seriously hurt.

The NBA has been trying to crack down on violence since Portland's Kermit Washington, then with the Los Angeles Alkers, seriously injured Houston's Rudy Tomjanovich with one punch during a brawl at the Forum two seasons ago.

Washington was fined $10,000 and suspended for 60 days.

There have been a number of other incidents of violence in the league this season in which O'Brien has levied fines.

George McGinnis of Denver was suspended for three games for intentionally running over referee Jess Kersey during a game.

Gene Shue, coach of the San Diego Clippers, was fined $3,500 and suspended for a week for swinging at official Dick Bavetta.

M. L. Carr of Boston was fined $1,500 for flagrantly elbowing Kansas City's Scott Wedman.

Bob Lanier of Detroit was fined $1,500 for punching Cedric Maxwell of Boston.

Adrian Dantley of Utah and John Drew of Atlanta were fined $500 each for fighting.

Official Earl Strom was fined $2,500 for punching fellow official Bavetta in the officials' dressing room during halftime of a game.