Isiah Thomas, the flashy all-star guard whose scoring and leadership helped the Detroit Pistons win the last two NBA championships, will have surgery to repair ligaments in his right wrist and will be sidelined three months, the team announced yesterday in Auburn Hills, Mich.

Thomas was examined Wednesday by wrist specialist Kirk Watson in Hartford, Conn. It was found that Thomas had damaged a ligament connecting two bones, causing the bones to separate.

Thomas apparently has been dogged by pain for nine months, but said he "thought it was a sprain that just wouldn't go away." Watson told Thomas on Wednesday he could continue to play with the pain through the season, then have the operation, and that was the course Thomas said he would take. But he was unable to shoot or pass right-handed in warm-ups before Wednesday night's 111-94 loss to the Celtics in Boston and contributed next to nothing in the game -- one-for-four shooting for two points with two assists in 22 minutes. Afterward, he changed his mind.

"He just couldn't go on," said Pistons General Manager Jack McCloskey. Thomas did not comment.

Watson will fuse three bones in Thomas's wrist in a surgical procedure he developed 15 years ago, and he said Thomas would wear a cast for at least eight weeks, followed by at least four weeks of rehabilitation before he could resume play.

Thomas's earliest return likely is April 23, two days after the end of the regular season. The decision to go ahead with surgery is in hopes of having Thomas ready for the playoffs, when Detroit makes a run for a third straight championship. The last team to win three consecutive league titles was Boston during 1963-66.

"He's looking forward to the playoffs," McCloskey said of Thomas, who has played this season despite eye, shoulder and groin injuries.

The Pistons said streak-shooting Vinnie Johnson would assume the off-guard spot in the starting lineup with regular off-guard Joe Dumars moving to point guard. Rookie Lance Blanks, who averaged 20.3 points a game in his senior season at Texas after transferring from Virginia, will be the first guard off the bench. The Pistons signed free-agent John Long, 34, who played for them for parts of nine seasons during 1978-89, to replace Thomas on the roster.

"I am prepared to go without him," Pistons Coach Chuck Daly said. "You don't have a choice. I've been contemplating this for a week because of all the injuries he's had."

It is also likely Dumars will take Thomas's starting spot for the Eastern Conference in the NBA All-Star Game in Charlotte, N.C., on Feb. 10. Thomas was voted by the fans to his 10th consecutive all-star game. He finished second to Chicago's Michael Jordan in the voting among guards, while Dumars was third.

Detroit drafted Thomas second overall in 1981 after he led Indiana to the NCAA championship as a sophomore. He has been a model of consistency, averaging 20 points and 9.8 assists in 10 NBA regular seasons and 21.4 points and nine assists in seven trips to the playoffs. Playing with injuries this season, he has averaged a career-low 16 points and was leading the league with 148 turnovers. He is third in the league all-time in assists and fourth in steals.