Sugar Ray Leonard was in strategic retreat in the first round before the punching of Daniel Gonzales, a no-nonsense Argentinian welterweight who wanted to win this fight today.And then Leonard nailed him.

He floored Gonzales with a single shot that belongs in the Louvre of right hands to the chin. End of Gonzalas. End of fight, in 2:03 of Round 1. And end of the widespread fiction that Leonard can box but can't punch. Leonard nailed that one, too.

The evidence was all over the Tucson ring in which Gonzales was staggering and falling twice. In his 66 previous professional fights, nobody had ever knocked him out or even off his feet. Leonard accomplished it today with the very first right hand he threw, this at the moment when he decided the Argentinian should no longer be allowed to dominate the fight.

The sudden right that turned the fight around for Leonard was not the final blow of the battle, but it was the climactic one. When the stupified Gonzales got up from a nine count, he was a feeble pigeon who went down again from a Leonard flurry.

When it seemed the referee was allowing the bout to continue, the Argentinian's corner people were crying "No, no," to the official, who eventually stopped it.

The 7,500 fans in the near-full arena and the ABC-TV network were shortchanged in everything except first-round excitement. They were also left in curiosity about the promoter's advertising that described the bout as a boxer vs. puncher affair, with Gonzales defined as the puncher.

Leonard admitted after the fight that he was a bit concerned by the tempo of the fight early in the round. "He came to fight," he said of Gonzales. "And he looked like the solid kind. I had to take the momentum away from him sometime."

Leonard added, "I hope they continue to say I can't punch. They're kidding themselves. I'm trying to be respected in this game. I've put so much of my life into it."

Gonzales, who got up from both knockdowns vacant-eyed, had little to say at the finish. Through an interpreter, he said of Leonard, "He hits good punch . . . and yes I am very surprised."

Leonard's handlers were jubilant. "No wear and tear on the body, and we're ready for another fight in April, with somebody," said Angelo Dundee, his coach-adviser. "I never saw him throw a better right hand."

It was a profitable afternoon otherwise for leonard. Counting his 50 percent of the live gate that was estimated at $130,000 and more than $200,000 in television pay from ABC, Sugar Ray was working at a wage of more than $160,000 a minute.

Today he was performing on network TV for the 15th time. First as an Olympic gold medal winner, and now as a top-rated challenger for the welterweight title, he is the boy that America watched grow up on television.

Gonzales, 29 and bearing no visible marks of his 66 fights, was moving in on Leonard with great resolution from the opening bell. He threw the first punch and had Leonard backing up, respectfully with follow-ups. Leonard's speed kept him out of trouble although he took some grazing shots from the aggressive Argentinian.

Leonard's advantage of four inches in height and four inches in reach over the stocky Gonzales was actually never exploited until near the end of the contest. It was then that Sugar Ray began to bring Gonzales up sharply with proper jabs.

He used the jabs to back the Argentinian into a neutral corner and then, on instinct, feinted with his left, causing Gonzales to make a move that brought his head perfectly in line with a right hand that is part of the old one-two taught in every professional gym.

Everything after that was academic. What Leonard had in front of him now was a numbed target for anything he cared to throw - until the referee intervened.

Roger Dale Leonard, Sugar Ray's heftier young brother, scored one for the family in a preliminary bout when he stopped Steve Delgardo, a local junior middleweight, in the fifth round. Leonard dominated the fight before it was stopped by the referee because Delgardo was bleeding from a badly wounded eye. CAPTION: Picture, Sugar Ray Leonard signals victory as referee Roger Yanez counts over Daniel Gonzales in first round. AP