Sugar Ray Leonard, demonstrating that touch of greatness and the big punch his trainers said would come out tonight, added the World Boxing Association junior middleweight championship to his collection when he scored a technical knockout over Ayub Kalule at 2:59 of the ninth round tonight.

Leonard sent Kalule, undefeated in his 37 previous fights, to the canvas for the first time in the Ugandan's career with two cracking right hands, a short left and a stunningly powerful short right.

Both fighters weighed in at 153 pounds.

There was some confusion at the finish because the round ended with Kalule on his feet after the mandatory eight count be referee Carlos Berrocal of Panama. But Kalule, knocked groggy by Leonard's potent punches, told the referee he did not want to continue. Thus, it was scored a technical knockout.

"I am satisfied," Kalule said after the fight. "They should have stopped it."

The most satisifed people among the 31,389 in attendance at the Astrodome had to be World Boxing Council champ Leonard and Thomas Hearns, who will fight Sept. 16, probably in Las Vegas, to unify the welterweight championship. Hearns was credited with a TKO in the fourth round over Pablo Baez in their WBA welterweight title fight earlier on the card.

Hearns and Loenard reportedly will be able to command a $20-million purse for that affair, though both men had to win tonight to assure such rewards.

Leonard had described Kalule as "an advanced amateur" earlier in the week, but when this fight had ended, Loenard said: "It's difficult to rate my toughest fights, but Kalule ranks in the top five . . . I anticipated a tough fight. I knew fully well that outside his family, the title was the most valuable thing to him."

But then again, so was Kalule's health valuable to him. His trainer, Borge Krogh, said that the referee asked Kalule "if he wanted to continue. Ayub said no He was hurt. But if he wanted to continue. Ayub said no. He was hurt. But is he know the round was over, I think he would have kept going. Auyb did not hear the bell."

Leonard did not want to hear that. "Do you believe that?" he asked in a postfight interview. "The guy was hurt. He should have no excuses. He's a great fighter."

The three official scorecards each had Leonard ahead after eight rounds. Judge Ismael Wiso Fernandez of Puerto Rico had it 78-75, and Berrocal and judge Camodia Cedeno of Panama each had it 78-76.

Leonard earned $2.5 million for his 30th victory and 25th knockout against one defeat. Kalule earned $150,000.

Leonard clearly was the better fighter -- and gymnast, as well. When it became apparent that Kalule had decided to retire for the night, Leonard did a spectacular front flip in the middle of the ring to celebrate the victory.

Leonard seemed in control through the first five rounds. Kalule, who covered up his face quite effectively, was not able to keep Leonard from working over his body, a factor Leonard said was decisive.

Leonard never seemed in trouble, and he demonstrated a portent of things to come when he scored impressively at the end of the fourth and fifth rounds. In the final seconds of the fifth, in fact, two right hands to the head did some damage, though Kaluly never seemed in jeopardy.

Kalule fought like a champion in the sixth and seventh, and both rounds seemed rather even, with Kalule having a slight edge. But all the while, Leonarde was working the body, setting up Kalule for the decisive ninth.

What he was not using, however, was much of a left. Leonard said he thought he pulled a muscle in his left hand in the fourth or fifth round, and did not press his luck by throwing many lefts. The right was so effective, it didn't matter.

Leonard said he had no idea what punches did the most damage in the final round. "I was throwing a great deal of uppercuts and kidney puches. When I see the tape, I'll be able to evaluate it."

Krogh said until his man was crippled by Leonard's two right hands, he thought the fight was going exactly the way he had planned it. "We thought it was going perfectly. He was at the stage then where we thought, physically, we were all right."

But Leonard ended that notion quickly, waiting until the end of the ninth before sending Kalule to the canvas and assuring what will become the richest fight in the history of boxing when he takes on Hearns.

Leonard, who weighted 153 pounds in his first step up to a heavier weight class, insisted once again after the fight that he never looked past Kalule to Hearns. Bring him out here. But still, the major issue is that I'm the new junior middleweight champion."

And he wants more. Leonard indicated tonight that he has his eye on the middleweight championship held by Marvin Hagler, who was in attendance here tonight.

"My ultimate desire is to go up against Hagler, the greatest middleweight in the world," he said.

In winning the junior middleweight title tonight, Leonard became only the sixth welterweight champion in boxing history to have won a title in a heavier weight class. Mickey Walker, Sugar Ray Robinson, Carmen Basilio, Emile Griffith and Wilfred Benitez had previously accomplished the feat. And for all true trivia freaks, Leonard also became the first Olympic champion to win a world championship in two weight classes.