Sugar Ray Leonard suffered what was described as a severe bruise to the knuckle on the middle finger of his left hand Thursday night when he defeated Ayub Kalule for the World Boxing Association junior middleweight championship.

Leonard insisted at a press conference this morning that he did not think the injury would prevent him from going through with his world welterweight championship fight Sept. 16 against Thomas Hearns of Detroit, a match that is expected to earn each fighter more than $10 million.

After scoring a technical knockout of Kalule at 2:59 of the ninth round, Leonard was taken to Houston's Park Plaza Hospital for X-rays. They did not show any fracture or break, according to Dr. Joseph Perlman, the Texas Boxing Commission physician who examined Leonard at the hospital.

"Most likely, it will not be a problem," Perlman said today. "Right now it does not look like anything significant. Yes, there is swelling, but that is not unusual. I also recommend that he be seen by his own physician when he returns to Washington, after swelling goes down. But basically, it is a severly bruised knuckle."

Mike Trainer, Leonard's attorney, said Leonard will be examined some time early next week by Dr. Carl MacCartee, an orthopedic surgeon who was one of Leonard's original financial backers.

"Of course we're concerned about it," Trainer said. "I'll fell a lot better next week when I know for sure nothing is wrong. I'll also be quite candid with you. I've told people who are actually spending money on the thing (the Hearns fight) not to go writing any big checks until we know for sure."

But Leonard, appearing at an 8 a.m. news conference before flying back to the Washington area, insisted "it won't hamper the fight in September at all . . . Yes, it is the same hand that gave me problems in Montreal (when he won an Olympic title in 1976). That time it was a problem because I had so many fights close together. This situation is better because I have time for it to heal.

"Just rest is the best thing for it now. After a few days, the swelling will go down and I can punch people in the head again."

Leonard was able to make a fist with his sore hand today, and the finger was not wrapped. The sore knuckle is the one at the base of the finger, and the swelling extends to the middle knuckle.

Leonard said he thought he sustained the injury when he hit Kalule in the head in the third round. It forced him to use his left primarily to body-punch the Ugandan and soften him up for the eventual final series of punches -- two sweeping rights, a left and then another short right that sent Kalule, now 37-1, to the floor for the first time in his boxing career.

On the unofficial clock, Kalule hit the deck with about 12 seconds remaining in the round, but he got up at the count of six. At the end of the mandatory eight-count, referee Carlos Berrocal of Panama waved his arms and stopped the fight.

Leonard was ahead on the three official cards. Berrocal and judge Carmodia Cedeno had Leonard ahead in rounds, 4-2, with two even. Judge Isarel Fernandez had Leonard leading, 5-2, with one round even.

Kalule said he did not know the round was almost over, that he might have wanted to continue if he could clear his head in the one minute break between rounds. "But I am satisfied. I told the referee it should be stopped."

Mogens Palle, Kalule's manager, insisted later that Berrocal asked Kalule in Spanish if he wanted to stop and that Kalule was simply shaking his head to clear away the hurt. "He would have recovered and fought on," Palle said.

"I hope Kalule and his people don't disappoint me by trying to make excuses," Leonard said, adding that he would give Kalule a rematch. "It was quite evident that the fight was over."

This morning it was also quite evident that the hype for Hearns-Leonard was already in mid-promotion form.

At 2 a.m. today, less than three hours after Leonard had disposed of Kalule, Emanuel Steward, Hearns' manager, stood in the lobby of the Astro Village Hotel and told anyone who would listen: "Tommy is going to destroy him with his left jab, and when the right hand comes, Ray will never see it."

Six hours later, Steward showed up at Leonard's press conference (Hearns did not) and went even further.

"I think Thomas can knock him out in five rounds," he said.

Leonard, sitting off to the side of the dais, cracked a large smile when he was asked to respond.

"This particular thing (Hearns absence) exemplifies the stereotyped fighter," he said. "I think Hearns should be here speaking for himself."

Earlier in the session, Leonard praised Hearns, describing him as a puncher in the top of his class. I'll take the fight straight to him, make him make mistakes, and then I'll correct them. I will carry Tommy Hearns to school, yes."

Both men also will carry considerable cash to the bank. Trainer confirmed today that Leonard made just under $10 million in his first fight against Roberto Duran and that "I would be shocked if he didn't make more in this fight."

Hearns already has signed a contract for the fight, and Trainer said he anticipated Leonard would sign a contract some time in the next week. And if hand heals properly, Leonard said he would begin training for the Hearns fight in about three weeks.

Ultimately, Leonard said, "My quest is for the middleweight championship. I've been saying I was going to quit since the first fight against Duran, and my wife still doesn't believe me. We'll see. I'm quite sure there will be other challenges."