Greg Benko defeated John Nonna in a fence-off for first place in men's foil at the Cherry Blossom Open fencing tournament at George Mason University last night.

The winner of the final bout, 25th on a program begun with 72 entries at 8 a.m., did not emerge until the final touch. Benko and Nonna were tied in the fence-off with four touches each: The winner would be the one with five touches against his opponent within six minutes.

Benko, 26, is from Melbourne, Australia, and a graduate assistant and and assistant fencing coach at Wayne State University in Detroit, where he coaches the women's team. He began fencing in Australia 15 years ago and has won the national title there 16 times.

Benko has competed in the last two Olympics. In 1972 he reached the quarterfinals in the men's foil. In 1976 he placed fifth.

"I rate that as my best achievement to date," he said.

Nonna, 30, is from New York City and "the only lawer in the finals." Earlier in the day he pulled a muscle in his shoulder and between bouts kept ice on the injured area.

Nonna took up fencing at new York University, "because I was charmed by it. I thought it was romantic." In the 1972 Munich Olympics he did "nothing" but at the world championships in Hamburg, West Germany, he reached the quarterfinals - first American to reach that point in 10 years. This year he will represent the United States at the Pan American Games.

Ernie Simon, 26, of Melbourne placed third in the finals, ahead of former Naval Academy All-America Ed Donofrio, 27, of Baltimore, who tied with Mike Marx, 20, of Portland, Ore.

Nikki Frank, 23, an instructor at Temple University in Philadelphia, won the women's foil following three fence-offs against Sheilah Armstrong, 29, of Jersey City. Frank also is bound for the Pan Am Games.

Debbie Cinotti, 25, of New York City placed third in the women's foil and Sharon Everson, 30, of Staten Island, N.Y., fourth.

The tournament continues today with epee and saber competitions beginning at 9 a.m.