Donald Curry knocked out Milton McCrory with a hard right to the jaw in the second round tonight to win the undisputed welterweight championship of the world.

Curry, the World Boxing Association and International Boxing Federation champion, knocked down McCrory with a left hook before finishing the World Boxing Council champion at 1:53 of the second round.

"I thought I was a lot stronger, so I just put it to him," said the 5-foot-10 1/2 Curry, who weighed 146 3/4, the same as the 6-1 McCrory. "But he was hitting me with some shots that made me realize he was out there."

Curry, who is 24-0 with 19 knockouts, took charge from the opening bell, scoring effectively to the body and hurting McCrory with two left hooks.

Curry was warned by referee Mills Lane in the opening seconds of the second round for a low punch but kept on the pressure and, at 1:25 of the round, dropped McCrory onto his back with a left hook to the face. McCrory struggled up at the count of eight, obviously hurt. Curry then threw a devastating right that left McCrory on the canvas for about 1 1/2 minutes.

"I started moving in after I hurt him in the first round, and I felt the fight was over," Curry said. "Milton didn't move a lot, he came to fight. I thought he'd change after I hurt him in the first round, but he came out and fought the same fight."

Said McCrory, "He is the best welterweight in the world. He caught me with a good punch. I didn't see it . . . I've been boxing 12 years and I was never knocked out, it's a funny feeling. I always thought I had a steel chin and couldn't be knocked out."

It was the first loss for McCrory, of Detroit, after 27 victories and one draw.

Curry joined middleweight Marvelous Marvin Hagler as the only undisputed champions in boxing.

Curry, 24, who got into boxing at age 8, said he soon would move into the junior middleweight (154-pound) class because "there are a lot of fighters there who will make me better."

His superb performance before 5,000 to 6,000 at the Las Vegas Hilton demonstrated that he is the best welterweight in the world.

McCrory, 23, also had indicated before the fight that he wanted to move to the junior middleweight class. It was not known how the defeat would effect his plans.

"Life works in mysterious ways," said McCrory. "I'll be back."

Curry and McCrory each earned $750,000 for the fight, which was carried on Home Box Office pay television.

Curry succeeds Sugar Ray Leonard as the undisputed 147-pound class champion. He won the vacated WBA title in 1983 after Leonard retired in 1982. McCrory replaced Leonard as WBC champion in 1983.