Chuck Michaels, the first-day leader in the modern pentathlon, added a mediocre shooting performance today to the "worst swimming time of my life" Sunday night and fell to 18th place with only the cross-country run remaining on Tuesday.

Despite his struggle, Michaels was hardly discouraged. To the contrary, he was bubbling while still accepting congratulations for his stunning victory in the individual epee fencing competition Sunday at the National Sports Festival.

Although Michaels, 24, is ranked only 11th nationally in epee, he defeated a field that included the top 20 in the United States. In the semifinal, he beat Cherry Blossom winner Steve Trevor, 10-3, and then won the title by defeating two-time national champion Lee Shelley, 10-5.

Although one local paper noted Michaels' victory as "surprising," the 5-foot-9, 148-pounder from Arlington, Va., fully expected to win, just as he foresaw his follow-up flops in the modern pentathlon.

"It was no surprise to me and I don't think my fellow pentathletes were surprised, either," Michaels said. "I had beaten all of them at one time or another. It was a matter of beating them all at one time.

"Until the Festival, I had never really had an opportunity to watch all the top fencers and pick out their weaknesses. Maybe 10 of the top 20 are pentathletes at Fort Sam Houston, but it's the other 10 I don't see very often. In boxing, you have time to feel out an opponent, but in fencing, if you're unfamiliar with him, it can be over before you see what he's doing.

"In fencing, you need financial capabilities to travel around and be in more competitions. As a full-time student (at Texas-San Antonio), I rarely got the chance to meet the best fencers.

"This year, though, I was selected to the World University Games team and I came here a week and a half early to train with the other top fencers. We fenced six to eight hours a day and I was able to see their weaknesses."

Michaels' first sports interest was swimming, and he was so good at it that it provided his entry into the modern pentathlon program, where he was introduced to fencing. He was not really in the swim for the pentathlon portion here, however.

Michaels has endured a crowded schedule since he first became involved in the modern pentathlon while a student at Washington-Lee High School. After returning from a 1976 clinic at Fort Sam Houston, the home of the U.S. Modern Pentathlon team, he sought sites in the Washington area where he could work on the sport's various skills.

Following competition in Poland, Italy and Finland, Michaels opted for a three-year military tour so that he could work on the modern pentathlon in earnest. But any hopes of qualifying for the 1980 Olympic team ended in a fencing match with Dean Glenesk, whose blade snapped on Michaels' shoulder and pierced Michaels' left arm.

Michaels' fencing fortunes have since improved. Although he says he has had 25 fencing coaches in seven years, he credits Kaj Czarnecki, the present modern pentathlon coach, with providing the guidance that led to this weekend's breakthrough.

Michaels is passing up next week's U.S. Modern Pentathlon Championships, which conflict with the University Games, to fence in that prestigious competition. As for 1984, however, he is uncertain of his priorities.

"With my results in fencing, I feel I have a high potential to make the 1984 Olympics as a fencer, certainly a better chance than as a pentathlete. This--beating the top 20 in the nation--has given me great satisfaction."

Andrea Godin, athletic trainer at George Mason University, won the gold medal at 105.5 pounds in women's Sombo wrestling at the National Sports Festival. She qualified for the Pan American Games Aug. 24-28 in Caracas, Venezuela.