The Washington Bullets placed Mitch Kupchak on the injured list yesterday and signed former University of Maryland player Lawrence Boston to a 10-day contract to take his place on the roster.

Kupchak, who is having back problems again, will have to miss a minimum of five games, but could be out indefinitely this season.

At the end of Boston's 10-day contract, he can be signed to another 10-day contract, signed for the remainder of the season or released. It all depends on Kupchak. Boston has averaged 15.4 points a game for Rochester of the Continental Basketball League.

The Bullets insist there is nothing seriously wrong with Kupchak and say he's expected to start working out again in the next few days. But with five games this week, beginning with a critical one against Indiana this afternoon at 1 at Capital Centre, the Bullets need all of the available bodies they can get.

Bob Dandridge is doubtful for today's game with his injured calf muscle and with Kupchak not able to play, General Manager Bob Ferry felt he had to make some sort of move now.

The 6-foot-8 Boston was a fourth-round draft choice of the Bullets in 1978. He played in Europe last season after being waived by the Bullets before the NBA season began.

Boston practiced with the Bullets yesterday.

"He played very well with us when he was here in camp and in the exhibition games," said Ferry, explaining why the Bullets signed Boston. "He's run our offense before, so he's familiar with it. And he has played very well in the Continental League. We're giving him a chance. We needed immediate help," Ferry added.

Kupchak underwent back surgery last summer to repair a herniated disk. He was activated Nov. 23, but never has returned to form this season because he has little strength. The soreness in his back prevented him from suiting up for the Bullets' last game, a 105-99 victory over Houston on Thursday.

Since being activated, Kupchak has played in 40 games and averaged 11 minutes, 4.7 points and 2.6 rebounds a game. He didn't play in eight other games.

The Bullets have lost four of five games to the Pacers this season, but today's encounter has particular importance. If the Bullets, 29-35, should win, they will move into a virtual tie with the Pacers, 31-35, for the seventh best record in the Eastern Conference. The top six teams make it to the playoffs.

The Pacers have been struggling lately and Coach Bob Leonard has been juggling his lineup. In their last game, Lonard started George McGinnis and Mike Banton at forwards, James Edwards at center, and Dudley Bradley and Johnny Davis at guards. They used their leading scorer and rebounder, Mickey Johnson, as the sixth man, but still lost to Altanta, 116-111.

The Bullets will play Detroit Tuesday and New Jersey Wednesday, both at Captial Centre, and then face the Pistons in Pontiac, Mich., Friday and the Celtics in Boston Sunday afternoon.