David Berkoff set a world record, and medal-laden Matt Biondi was the top qualifier in the 50-meter freestyle, but the United States couldn't avoid another Olympic disaster at the pool Saturday.

Berkoff swam underwater on his back for about 35 meters before popping to the surface with a big lead in the final heat of the 100 backstroke.Berkoff was timed in 54.51 seconds, smashing his own world record of 54.91 set last month in the U.S. trials.

"I didn't think I was going that fast, but I knew I was in front," Berkoff, of Willow Grove, Pa., said. "I expect to go faster in the final. I'll have to because Igor Poliansky is a great competitor."

Berkoff said his unconventional start gives him an advantage, but he added, "I don't think it should diminish what I'm doing. I've trained very hard, and my second 50 meters is much better this year."

Poliansky, gold medal winner in the 200 backstroke, was the second qualifier in 55.04.

In an earlier prelim, the U.S. swim team suffered a setback when Mary Wayte of Mercer Island, Wash., was disqualified from the 200-meter individual medley for an illegal kick.

Wayte would have been the third-fastest qualifier for the event with a time of 2 minutes, 15.71 seconds, but two judges ruled that she used a butterfly kick on the 50-meter breaststroke leg.

The United States has only three individual gold medals in 15 swimming events, and all of them have been won by Janet Evans and Biondi.

"It was a judgment call, but I understand these officials judge meets maybe once a year," Wayte said. "Obviously, they're not familiar with recent breaststrokes because I'm not the only one who does breaststroke that way. I've been doing that kind of breaststroke since 1983, and I've never been DQ'd for that reason."

Wayte said her feet tend to drop on her breaststroke kick, "but there's no propulsion from it. They counted that dropping as a dolphin kick."

Ironically, Wayte's disqualification opened the door for Whitney Hedgepeth of Petersburg, Va., who was the eighth and final qualifier in 2:17.45.

Elena Dendeberova of the Soviet Union was the top qualifier in 2:15.30, just .41 ahead of Wayte.

Biondi, with three golds, a silver and a bronze in five events, was the top qualifier for his sixth race, the 50-meter freestyle.

Biondi, looking to equal Mark Spitz's record for swimming medals in seven events, was timed in 22.39 for 50 meters.

Biondi, of Moraga, Calif., was followed by Gennadi Prigoda of the Soviet Union in 22.57.

Tom Jager of Topanga, Calif., the world record-holder at 22.23 tied for the third qualifying spot with a clocking of 22.61. Dano Halsall of Switzerland also was timed in 22.61.

The United States was the No. 2 qualifier in the women's 400 medley relay behind East Germany. The team of Betsy Mitchell, Tracey McFarlane, Mary T. Meagher and Dara Torres was timed in 4:10.38; East Germany had 4:08.53.

China, a medal contender, would have been third in 4:11.66 but was disqualified for an early start on the third leg.

Michael Gross of West Germany, who won two individual golds and one silver in the 1984 Olympics but has been shut out of an individual medal in Seoul, was the top qualifier in the 200 butterfly. Gross was timed in 1:58.09, while Anthony Mosse of New Zealand was second in 1:58.71. Melvin Stewart of Fort Mill, S.C., was the sixth qualifier in 1:59.78.