David Berkoff of Harvard broke the American record in the 100-yard backstroke for the fourth time this year, winning in 47.02 seconds Friday night at the NCAA Men's Swimming and Diving Championships.

Berkoff, a 1988 Olympic silver medalist and world record-holder in the 100-meter backstroke, lowered the U.S. mark of 47.33 he set March 4.Berkoff, from Huntington Valley, Pa., is the only Harvard swimmer to win an NCAA title in the last 28 years. He plans to retire after the NCAA meet.

"It has gotten to the point that I have done everything I wanted in swimming," Berkoff said. "I know it's time to get out. I don't get excited about swimming now."

Berkoff was deep underwater most of the race, breaking the surface only for turns. His "human torpedo" style has been outlawed by international swimming officials but is legal in NCAA competition.