The Boston Celtics opened the second half by scoring seven straight points against the Atlanta Hawks today, and the deciding game of this best-of-three NBA playoff series was all over but the biting.

The Celtics advanced to the Eastern Conference semifinals with a 98-79 victory, during which which Atlanta center Tree Rollins bit Boston guard Danny Ainge in a free-for-all in the third period. Ainge, who needed five stitches to close the ensuing wound on the middle finger of his right hand, is questionable for Wednesday night's game here against Milwaukee in the opener of the best-of-seven series.

Today, the Hawks could not match the Celtics' overall intensity. The best example of Boston's determination was provided by Larry Bird, who scored 26 points, had nine rebounds and nine assists, and limited the Hawks' Dominique Wilkins to one field goal with suffocating defense.

Early in the second period, with Boston 12 points ahead, Bird raced to the midcourt line and averted a back court violation by diving to tap the ball to a teammate, crashing to the court well beyond the line in the process. When Cedric Maxwell converted Bird's effort into a basket, the usual Boston Garden sellout crowd of 15,230 cheered loudly in appreciation.

"We knew we had to win," Bird said. "We didn't play well in Atlanta, but today was a whole different atmosphere. The crowd was involved and everybody on this team responded with a great effort."

With the loser heading for a vacation, both teams played hard, and officials Darell Garretson and Paul Mihalak had difficulty maintaining order. In the third period, there was no chance, as an exchange of elbows between Ainge and Rollins quickly escalated into a free-for-all that involved all the players plus Garretson and Hawks Coach Kevin Loughery.

Ainge earlier had been involved in shoving incidents with both Rollins and Mike Glenn. After Rollins stuffed a shot to reduce Boston's lead to 68-52, he started down the court. Ainge, 6-5 and 188 pounds, waited for Rollins (7-1 and 235) and started to move into him with a shoulder. Rollins, however, threw out his left elbow and rocked Ainge on his heels.

Rollins staggered to one knee and, as he rose and headed back toward Ainge, the Celtics' multisport star used the tackling ability of his high school free safety days to put Rollins on his back.

Atlanta's Rudy Macklin jumped on Ainge, Bird piled into Macklin and soon all the players were involved. While Ainge was underneath the pile, he was bitten on the middle finger of his right hand. The flesh, bearing obvious toothmarks, was exposed to the tendon.

Ainge and Glenn were ejected; Rollins stayed in, to be taunted by the Boston fans until he finally fouled out and left with his right fist raised in the crowd's direction.

"In my estimation, Ainge and Glenn were the first two fighting," Garretson said. "They had an altercation on the base line on the Tree dunk. The first thing I saw later was Ainge going toward Tree Rollins. We will always allow a man to defend himself, which was why Rollins was not ejected.

"But it all happened so quickly. We had thousands of people rolling around on the floor, including myself. We'll look at the videotapes later and see it all."

"I came off a pick and he elbowed me," Ainge said. "Then he elbowed me again and I couldn't let him get away with it. The officials weren't doing anything about it. It wasn't something I thought about; I'd just had enough.

"Then when I was in the pileup, I had my right hand free and was trying to get away and he bit me. I guess somebody had his arms and he couldn't get at me, so he did that."

Asked if he bit Ainge, Rollins said, "Maybe."

He said the incident had its roots earlier when "he hit me with a punch. I told Darell and he didn't do anything about it. Then he hit me a second time and I wasn't going to turn both cheeks."

Boston trainer Ray Melchiorre said Ainge "has good range of motion in the finger." Meelchiorre said Ainge's finger was not bitten to the bone but "you can't get much closer."

Bird said, "I thought Danny Ainge was a pretty tough guy because it took three of them to hold him down and one to bite him."

Ainge put the Celtics ahead to stay on the game's first score and his only field goal, a three-pointer from the corner after 32 seconds. Then Boston utilized three of Atlanta's seven first-period turnovers to expand its advantage to 11-2 less than three minutes from the start.

Atlanta made a brief run late in the first period, reducing the margin to 26-23. But the Hawks took some bad shots while Boston scored six straight points before the buzzer.

Substitute Kevin McHale scored 14 second-quarter points, as well as five rebounds, in helping the Celtics to a 59-45 halftime lead.