It may have taken six long years, but with Sunday's 102-99 victory over the Boston Celtics in Game 4 of their Eastern Conference semifinal series, the Detroit Pistons finally reaped the benefits of one of the more disastrous draft picks in the team's history.

Picking fourth in the 1979 college draft, the Pistons were bilked by the Milwaukee Bucks, who told anyone listening that their choice with the fifth pick in the opening round would be Greg Kelser of Michigan State. Worried about the adverse public reaction if they failed to take Kelser, Detroit grabbed the local product, only to see the Bucks jump at guard Sidney Moncrief of Arkansas, the player they had wanted all along.

Moncrief, a three-time all-star and twice the NBA's defensive player of the year, quickly established himself as one of its most stellar talents. Kelser struggled from the start of his career. In 2 1/2 years, the forward never showed that he merited his lofty draft status.

Midway through the 1981-82 season, Kelser finally was dealt to the Seattle SuperSonics. In return the Pistons received guard Vinnie Johnson. He became a solid reserve, and the trade's value was never more evident than in the fourth quarter of Sunday's game against Boston.

Averaging just under 10 points a game against the Celtics entering the contest, Johnson scored a career-high 34 points, including 22 in the final 12 minutes, in leading Detroit to the series-tying victory. The series will resume Wednesday night in Boston.

After making 10 of 11 shots in that quarter, Johnson, the seventh pick in that 1979 draft out of Baylor, seemed ready to give credit for his performance to everyone but himself. "I'm just happy that we won," he said. "The fellas were looking for me and they were setting great picks."

In his most selfless act, Johnson also gave credit for his effort to the Celtics' Dennis Johnson, his victim for the majority of the fourth quarter. The two were teammates on the SuperSonics during the 1979-80 season and the Pistons guard said, "Playing with him helped me learn what he likes to do on defense, how he likes to play people."

In the Celtics' locker room though, an almost shellshocked Dennis Johnson brushed aside the notion. "Is that his way of saying thanks?" asked Johnson, generally considered one of the NBA's better defensive guards. "Really, I may have told him a couple of things but Vinnie isn't nearly the same player he was during the time we were together."

One thing that hasn't changed is Johnson's remarkable physique. Standing 6 feet 2, Johnson weighs 200 pounds, all of it muscles upon layers of muscles. He says he's never lifted weights in his life but there's no question about his strength.

"There's nothing that he can't do out on the court," said back court mate Isiah Thomas. "He can shoot the jumper and he drives and you can't stop him. In fact, you just want to get out of the way."

According to teammates, Johnson is Detroit's preeminent practice player, a status attained by many others who are unable to transfer those same skills into a game situation.

That isn't the case with Johnson, who said today he could recall only one performance that could approach his game against Boston. "Once when I was at Baylor, I scored 45 points in a game against San Francisco when they had (New York Knicks' center) Bill Cartwright and some other great players," he said. "But then the pressure wasn't as great as it was in this game. Every shot seemed like it meant something."

That's probably because it did.

Someone asked Dennis Johnson if anyone had ever taken advantage of him like that. "Yesterday, in fact," he said. "M.L. Carr won $50 from me playing cards. On the basketball court? I don't know. That's one stat I've never tried to keep track of." Surgery for Lever Associated Press

DENVER, May 6 -- Guard Lafayette Lever, who suffered a knee injury in the final seconds of the Denver Nuggers' 131-123 loss Saturday to the Utah Jazz, was to undergo arthroscopic surgery tonight.

A spokesman for the Nuggets said if no major damage is found, Lever would be out seven to 10 days, meaning he would miss the remainder of the Utah series even if it runs the full seven games. If a significant tear inside the knee is found, he could be out further.