Bullet forward Mitch Kupchak underwent surgery on his damaged right thumb yesterday and will be lost to the club for a minimum of six weeks.

The operation at Sibley Hospital repaired a torn ulnar collateral ligament in the thumb, hurt Wednesday in a game against Golden State and then reinjured Friday night against the Los Angeles Lakers.

Team physician Dr. Stanford Lavine, who performed the surgery, said Kupchak would be in a cast for four weeks before beginning rehabilitation. He could leave the hospital as early as today.

Phil Chenier, who also is at Sibley for treatment of a back problem, was placed on the injured reserve list by the Bullets prior to Sunday's game at Phoenix. He will have to miss at least five games, meaning he won't be able to return before next Tuesday, when the Bullets play at San Antonio.

General manager Bob Ferry said he still did not know whether Chenier would be out for more than another week, although it took the veteran guard a month to rebound from a pre-season back injury. And he said he was not close to making any trades or signing any free agents to fill the two vacant roster spots.

"I've been on the phone all day talking to people" he said "but we aren't that close to doing anything yet.

"I'm still trying to determine how long Tom Henderson and Kevin Grevey are going to be out. If they are back soon then we haven't got that big a guard problem."

Henderson who sprained an ankle in the Golden State game and has not played since, said yesterday he will try out his injury in warmups prior to tonight's 8:05 game against Detroit at Capital Centre. If it feels all right, he will play. Otherwise the Bullets again will suit up just seven men.

"I've got to" he said. "We need some help and I've got to try to come back if I can

However, Lavine said Henderson's ankle was still swollen and that he was very questionable for the game.

Grevey's hamstring pull is responding to treatments but it is doubtful that he will be available before Sundays game against Los Angeles. The Bullets also play Chicago here on Thursday and at Chicago Friday.

Another guard, Larry Wright, has lost seven pounds in a week-long battle with the flu. The already-slight Wright said he was starting to regain his strength but still did not feel 100 percent.

The starting Bullet guards, Wright and rookie Phil Walker, score only 24 points in the loss to Phoenix Sunday while the starting Sun guards had 49.

Although Ferry said the team would play with nine men for an extended period, "and not just add someone for the heck of it," it seems likely the Bullets will acquire at least one player especially if Chenier responds more slowly than expected.

With Kupachak out, the Bullets are left without their No. 1 reserve strong forward (backing up Elvin Hayes) and No. 1 reserve center (backing up Wes Unseld). And they suddenly find themselves trying to make up for the 14.8 points and 7.2 rebounds Kupchak averaged per game.

For the present coach Dick Motta plans to use rookie Greg Ballard, who has been a small forward, as Hayes' backup. Joe Pace is the only reserve available to back up Unseld but his status has decreased since he walked off the team in early December. Hayes, however, can move over to center.

"If we get Kevin back, he can play forward," said Ferry. That would free Ballard to back up Hayes, but until Chenier is available, Grevey would be the only player on the team who naturally mans the big guard position.

"We knew Mitch might be lost for a while, but you always hope you might be wrong," said Motta, who found out early yesterday morning that Kupchak would have the operation. "We will miss him, he's a very valuable player and he gives you the kind of lift off the bench that is hard to replace."

Kupchak's operation climaxes an incredible 10 days of events that began with the Bullet's convincing triumph over Portland Jan. 13.

"We were very happy with this club 10 days ago," said Ferry. "We were right where we wanted to be. We were one of the top four teams in the league."

Since then, the Bullets have lost four straight, their longest winless streak of the season: they've fallen two games behind San Antonio in the NBA Central Division race after leading since Dec. 4, and they've had four players sidelined by injuries.

With nine of their next 13 games on the road, where they've lost nine times in the last 11 tries, the Bullets are fearful they could be far behind the Spurs before regrouping. And they realize now that the earliest they can expect Kupchak back is early March, and that is probably being optimistic.

Ferry said that he was working at a disadvantage. "No one is rushing to help us in the league and we've got the Eastern League and maybe two other small leagues we are working against trying to get someone.

"But I'm really always looking for someone to help us at any time. It may seem more urgent now but it would have been easier getting someone a month ago."