Joe Pace, the third-string center for the Washington Bullets who had played out his option, signed a multi-year contract with the Boston Celtics yesterday.

The 6-10 former Coppin State University star, who was picked by the Bullets in the second round of the 1976 college draft, had been unhappy about his lack of playing time. He had played behind starting center Wes Unseld and backp Mitch Kupchak.

Last season Pace played just 438 minutes in 49 games, scoring 191 points and grabbing 134 rebounds.

"We just didn't have enough minutes for a third-string center," said Bob Ferry, Bullets general manager. "Bernie (Bullet Assistant Coach Bickerstafff) and K. C. Jones (Celtic assistant coach) had been talking about Pace.

"The Celtics wanted someone to back up Dave Cowens after they lost Kevin Kunnert." Kunnert, the proposed Celtic backup center, went to San Diego in a multiplayer trade earlier in the summer.

Pace walked out of his rookie training camp for one day because he was upset over his play and did not think he was going to make the team.

He repeated the action the following fall, staging a four-day walkout from training camp, refusing to say why on his return.

Pace transferred to Copping State after playing two years at Maryland Eastern Shore. He led Coppin to the NALA championship in his senior year and was selected as most valuable player in that tournament.

The Celtics must compensate Washington for Pace. Ferry said he had no special preference as to whom Boston might send here. The Celtics might also offer the Bullets a draft choice.

"It's up to the Celtics," Ferry said. "They decide who to send. If the decision is unsatisfactory to me, then the commissioner will decide."

Pace's departure leaves the Bullets with Unseld and Kupchak in the middle plus second draft choice Dave Corzine of DePaul, Corzine has not signed.

"Pace has the potential to be one of the better starting centers in the league, with maturity," Boston Coach Tom Sanders said. "He has outstanding shot-blocking ability to go along with excellent speed."