Sugar Ray Leonard was the focus of a two-part show Thursday night, and the fighter is $40,000 richer for his performance.

Leonard showed a record crowd of 15,272 that he is just about a complete boxer, ready for bigger game. And Capital Centre showed on its Telscreen that instant replays of officials' decisions are feasible.

The latter was a lesson for the National Football League, which has been debating for some time the possibilities of using replays to assist on disputed calls.

Leonard knocked out Bobby Haymon of Cleveland with a left hook to the head after the bell ending the third round. Haymon, however, would not have been able to continue if he had been given an hour's rest.

It was an illegal punch but probably a merciful one for Haymon. Five shattering punches before the final sequence left Haymon virtually helpless. He had shown no indication after the middle of the third round that he was going to be able to hold off Leonard, who had just begun to take full command of the bout.

Capital Centre showed the whole fight on Telscreen, and flashed back instant replays of the controversial punches at least twice.

Because there was no narration accompanying the picture on he screen and because the sound of the third-round final bell might not have been heard because of the crowd noises also picked up by Telscreen, the fans might not have been able to pinpoint the timing with the bell and Leonard's last two punches.

A Centre representative invited members of the media to view replays after the fight. A slow-motion replay showed that Leonard had started a right cross to the head before the bell sounded, and landed it after the bell. A left hook to Haymon's head followed the right.

At ringside, referee Harry Cecchini said Leonard did not punch Haymon after the bell.

Hod the referee decided Leonard hit Haymon after the bell, he could have warned him, taken a point or two away from him, or disqualified him under Maryland boxing rules.

Without seeing the Telscreen ersion, Haymon's manager, Dominic Polo, said he was going to file a complaint about the referee's decision with the Maryland State Athletic Commission. Jack Cohen, secretary to the commission, said yesterday no complaint had been filed and that Polo "calmed down" later Thursday night.

"I though the replay shoed different than what the media said," Cohen said. "I don't know if we can do anything now. I see no reason for any action because, one, the referee stated that all Leonard's blows were delivered prior to the bell, and, two, we would be back to the football problem of looking at a reply before making a dccision. It would be a tough decision."

Future Leonard bouts have been set up for Utica, N.Y., in May, Baltimore in June, Boston in July, Hartford in August, Cleveland in September and Baltimore in October. Leonard may appear on television in May or June.

Cohen disclosed that Thursday's bout set a Maryland indoor record gross of $97,433,50, with a net of $88,525.22. The attendance, not counting sky boxes, which are rented on an annual basis at Capital Centre, was 14,268, and the actual paid attendance was 12,902.

Michael G. Trainer, the Silver Spring attorney who handles Leonard's financial affairs, said his client figures to have had his best non-television payday Thursday.

With the accounting incomplete, Leonard is expected to be paid between $35,000 and $40,000.

The former Olympic champion earned $42,500 for his first pro bout, but $10,000 came from television rights sold to CBS. He was paid more than $85,000 for his bout on the Ken Norton-Jimmy Young show in Las Vegas, but it was on television in which, incidentally, he was told that the ratings for the time he was on were higher than for the main bout.

Trainer said he did not want Thursday's bout on television because he does not want Leonard to become overexposed.

Trainer said there was a three-part financial arrangement with Capital Centre.

"We had a flat guarantee (believed to have been $10,000): a stipulation that Ray would receive the first money of the net gate to a certain extent, plus 50 percent of income after that point. We were almost partners."