A half-hour earlier, as he stood on the diving board, Greg Louganis had joined the crowd in laughter. Now, a few minutes after his victory in the three-meter springboard competition at the National Sports Festival Thursday night, Louganis was blushing.

"I'm sorry, Coach," Louganis said to Ron O'Brien, his coach at Mission Viejo, Calif., after admitting that he had laughed at the height of competition.

Louganis, 23, has been the dominant diver in the world ever since he won an Olympic silver medal in Montreal in 1976. He has also been one of the nicest.

A year ago, after winning the platform event at the Festival in Indianapolis, he pulled his longtime rival, second-place Bruce Kimball, onto the winner's platform with him. It was an acknowledgment of Kimball's return from a serious automobile accident. It also was a typical gesture by a man who commands the respect of those he defeats so frequently.

"We've known each other for about 10 years and we both go at it the best we can and we're trying to beat each other but, at the same time, we're not against respecting what the other person's done," Kimball said.

In that area, diving certainly differs from most sports. After the springboard competition here, the women exchanged kisses and the men shook hands, thereby duplicating what they had done beforehand. If there were any mean streaks below the surface, they were well-hidden.

Returning to the subject of Louganis' blush, as he prepared for his ninth dive of the competition, the announcer intoned, "Reverse 1 1/2 somersault with 3 1/2 twists, degree of difficulty 3.3." The crowd, either in disbelief or sympathy, laughed and Louganis joined in.

"We had new dives approved in September and it was felt that a lot of them required a greater degree of difficulty than 3.0, so the limit was raised to 3.5," Louganis explained. "But a lot of people don't know we have broken the 3.0 barrier, so they were oohing and aahing. I thought to myself, 'Are you sure you'd like to do this dive?' "

Divers such as Louganis and Kimball have explored areas previously reserved for stunt men and it was the difficulty of what he was attempting that carried Louganis to victory here over teammate David Burgering.

"Look at the raw scores and you'll see that David was more consistent; I won because my dives were more difficult," Louganis said. "I was really nervous, this being the Pan Am trials, with only two going to Caracas. It was a strong field, anyone could be up there, and I was shaking pretty much."

This confession came from a man who in August in Ecuador won the springboard and platform titles at the World Aquatics Championships. Although one must respect his innate honesty, it is hard to imagine that Louganis is afraid of anything--unless it is the ceiling of the Air Force Academy pool.

In 1979, during practice for the Sports Festival, Louganis struck the ceiling while performing a reverse dive off the 10-meter board. He subsequently declined to participate in the platform competition and agreed to try it this time, in trials that began today, only when Air Force Academy officials took a chunk out of the ceiling, providing three more feet of elbow room.

"I jumped up the other day and put my hand through where the roof had been," said Louganis, whose 31-inch vertical jump obviously has something to do with his success.

The diving competition here attracted a large, enthusiastic crowd, just as it did in Indianapolis a year ago. Asked about the surge in the sport's popularity, O'Brien said, "The credit has to go to Kimball and Louganis. Their rivalry has attracted extensive media coverage and created more interest in diving.

"We're still No. 1, but we're just that far ahead of the People's Republic of China (thumb and index finger held about a half-inch apart)."

Louganis looked solemn for a moment. You could almost imagine him shaking with a case of nerves in Los Angeles in 1984, just before claiming a couple of gold medals.