New Jersey is assured of finishing ahead of the Washington Bullets after coming from behind tonight to race past lethargic Boston, 113-96, on the strength of a 27-point performance by Buck Williams.

The Nets' fourth straight victory gave them a 43-38 record going into their finale Saturday night in Detroit. Even if they lose and the Bullets beat Atlanta Sunday at Capital Centre to match New Jersey's record, the Nets will get a higher playoff spot because they won the season series from Washington, 4-2.

The Nets' first victory in six tries against the Celtics this season was made easier by Boston Coach Bill Fitch's preseason substitution pattern. Larry Bird, for example, did not play in the first or fourth quarters, finishing with 12 points.

"Bird didn't play well enough to go back in," Fitch said when asked why his all-star was on the bench after the Nets scored the last eight points of the third quarter to take a 90-78 lead into the final period.

"He was like the rest of his teammates tonight," Fitch said. "He is human and mortal. He came out because his minutes were up."

Fitch admitted that it has been difficult to keep his players' intensity up this week after they clinched their third consecutive Atlantic Division title. After rallying to beat the 76ers in Philadelphia Sunday, the Celtics lost at Chicago and struggled to beat Milwaukee in Boston.

"I'm just trying a lot of different combinations," he said. "It takes a little of the monotony out of the final games. I haven't started the same lineup in any quarter all week."

Tiny Archibald played the entire first half and had 12 assists, then didn't play after intermission. After falling behind by 12 points with 5 1/2 minutes to play, the Celtics went with Rick Robey, Eric Fernsten, Gerald Henderson and rookies Charles Bradley and Danny Ainge.

"We have to put this game in perspective," said the Nets' Len Elmore, who usually does. "They didn't start their regular players and probably didn't have their usual intensity. After beating us five in a row and playing on the road, it's understandable if they weren't up for the game."

With Archibald leading the way, Boston played well in the first quarter, taking a 27-19 lead. The Nets came back, with Buck Williams getting nine points and four rebounds, to pull within two, 33-31, at the end of the period.

Bird, Robert Parish (21 points) and Henderson entered the game at the start of the second quarter, and Parish scored six points as the Celtics moved out to a 38-33 lead. A few minutes later, Bird scored six straight to make it 49-43, but New Jersey rallied to score the last three points of the half, reducing its deficit to 57-54 at intermission.

"We played better than to only be up three points at half," Fitch said. "But in the third quarter, New Jersey beat our butts. They controlled the boards and we had our veterans in then."

Naturally, New Jersey Coach Larry Brown looked at the game differently.

"This is as good as we've ever played," he said. "We just can't play any better. The Celtics are a great team, they're so unselfish, and to beat them we have to play our best game.

"Buck was just sensational," he said after the rookie from Maryland came within two points of his season high and got five of his 12 rebounds off the offensive boards. "I'm so proud of what he's done. We wouldn't be where we are today if it wasn't for Buck."

Williams already was thinking about the upcoming playoffs. The Nets have clinched at least fifth place, which means if they win the miniseries, they will face the Celtics in a seven-game series.

"If we have to play the Celtics in a seven-game series, we didn't want to go in zero and six against them in the regular season. Now they really have to think about us. Now they know we can beat them."