After appearing tentative during the first round, S.T. Gordon took the World Boxing Council cruiserweight title today, battering defending champion Carlos De Leon with more than 50 punches before referee Carlos Padilla stopped the bout 2:51 into the second round.

Doctors stitched up De Leon's lower lip, but the fighter was not seriously injured.

Gordon, 23, from Los Angeles, improved his record to 22-5, with 20 knockouts. De Leon, 23, of Puerto Rico, fell to 30-2-1. It was his third fight since he won the title for this weight class, one step below heavyweight, from Marvin Camel of New Orleans on Nov. 25, 1980.

De Leon was the aggressor in the first round and appeared frustrated at times when Gordon tied him up.

The second round opened in similar fashion until Gordon threw a combination of punches that momentarily stung De Leon. Gordon then pursued and knocked down the defending champion with a three-punch combination that ended with a sharp left catching De Leon on the chin.

After De Leon returned to his feet, Gordon attacked relentlessly and drove De Leon into a corner, where he unleased a ferocious flurry of punches. De Leon appeared to remain standing only because he was leaning against the corner post.

De Leon staggered across the ring, and, after another brief series of punches, blood began flowing profusely from his mouth. The referee then stopped the fight.

"I tried to allow him to recover," said Padilla. "This was a title fight. You have to give the guy a chance, but when he staggered to the middle of the ring, I knew he was out on his feet."

Later, interviewed on the CBS Television network, Padilla said, "You know boxing. This is a game of knocking your brains out . . . You stop a fight when the boxer is helpless. But he was trying to avoid the punches; he was rolling the punches."

Gordon, who was disqualified for not fighting hard enough in the sixth round of a fight against heavyweight contender Gerry Cooney in 1977, said he would like to move up into the heavyweight division after defending his new title a few times.

"I want Larry Holmes or Mike Weaver," he said. "I want their big bucks. That's my dream."

Gordon said he felt the fight should have been stopped sooner. "He was out on his feet. But he's the champion and he has plenty of heart."