Tommy Hearns went into his welterweight title fight with Sugar Ray Leonard with a reputation as a knockout specialist whose boxing skills were suspect. Now, as he looks forward to his promising career, there is no doubt about his ability to box.

After being rocked in the sixth round, when his knees buckled following a stinging left hook from Leonard, Hearns made a remarkable recovery and boxed with his opponent from the ninth through the 12th.

"I know I can come back," Hearns said today. "If Ray gives me a rematch, I can win it.

"To get my championship back, I'll have to fight a better fight, but I can do it. Everybody has to lose sometime. To be a great champion, you have to be able to come back. I'll put on a better show next time.

"I think I deserve a rematch," Hearns said at a press conference. "I think the people will pay to see us fight again. They saw a great fight . . .

Angelo Dundee, Leonard's manager and cornerman, said it was the first time Hearns ever had backed up. The previously undefeated champion from Detroit was always the aggressor in his 32 previous bouts. Most of the prefight speculation centered around whether Hearns could box with Leonard.

Many felt that if Hearns didn't get a knockout, his chances of wining were slim. After losing the sixth, seventh and eight rounds, Hearns rallied, the spring returned to his legs. He backpedaled, moved laterally and generally stayed out of Leonard's reach. While avoiding the stalking Leonard, he managed to score well enough with jabs to win rounds nine through 12.

"Thomas was hurt in the sixth when both fighters threw a 1-2 combination. Then Ray followed with a good left hook," said Emanuel Steward, Hearns' trainer-manager. "He beat Thomas to the punch.

"From that point Thomas never really recovered," Steward continued. "He came back boxing well and picking up some points, but when the opportunity presented itself, Leonard took advantage.

"At the end, Leonard turned out to be Frazier and Tommy was Ali."

Steward was referring to the three memorable Joe Frazier-Muhammed Ali fights when Frazier was the relentless slugger and Ali the evasive boxer.

Two of the things that Steward said he learned from this fight were that his man could take a punch and that he can box with Leonard.

"I saw Leonard outboxed and I had never seen that before," he said. "The tide continually turned. It was a great fight."

Hearns admitted he was frustrated in his attempts to land a solid right to Leonard's jaw, something that had put away 30 of his 32 previous opponents.

"I wasn't able to hit Leonard with my best shot," he said. "I wasn't able to get my weight behind it. Ray was always moving left."

Some ringside observers counted only three right-hand punches by Hearns after his sixth-round beating. Why would an unbeaten champion put his best weapon in mothballs?

"I only shoot my right if I think I can land," he explained. "Some people have asked if my ribs were broken from that shot in the sixth. They were no problem."

Meanwhile, much of the speculation concerning these fighters' future centered around what weight class they will be in for their next match.

"Hearns never has had any problems making 147 pounds," Steward said. "It will be easy for him to fight as a welterweight, a junior middleweight or a middleweight."

Hearns, 6 feet 2 1/2, weighed in at 145 pounds for the fight; Leonard was at 146. Leonard said he was up to 152 by fight time, but lost seven pounds during the bout.

"I'll be a full-fledged middleweight soon," the 25-year-old Olympic gold medalist from Palmer Park, Md., said. Leonard already owns a share of the junior middleweight title after beating previously undefeated Ayub Kalule last June in Houston.

The present middleweight champion is Marvin Hagler, and neither Leonard nor Hearns is particularly eager to step into the ring with him now.

"I don't know who I will fight next, but it won't be Hagler," Hearns said. Leonard said that the longer he waits to fight Hagler, a 29-year-old knockout specialist from Brockton, Mass., the better his chances will be.

From what was said today, it seems obvious that there will be a Hearns-Leonard II. The only question is when. Leonard wants "a tuneup" before his next major bout. Leonard was asking today for Aaron Pryor, the junior welterweight champ.

Despite a record of 25 knockouts in 27 fights, Pryor, at 5-6, does not present the physical problems of Hearns and Hagler. Leonard hardly figures to absorb the same sort of blows he has in his two fights with Roberto Duran and one with Hearns.

For now, Hearns said, he will take a vacation and let Steward make the arrangements for any upcoming fight.