While most of the Harvard men's swimming team was cruising through the weakest part of its schedule, yardling aquaman Dave Barnes was representing the United States in an international meet held earlier this month in Rio de Janeiro, Brazil.

Along with 13 other college and high school students. Barnes competed against the national teams of Brazil and the Soviet Union in an invitational competition sponsored by the Brazilian swimming federation.

The Mission Viejo, Calif., native stroked to two third-place finishes and one fourth, but was denied a chance to swim his two best events--the 200 and 400 individual medleys--when meet officials cancelled the events. Barnes is currently ranked 18th in the world in the 200 and 25th in the 400.

He said yesterday that the Brazilians nixed the events because their best medleyist. Ricardo Prado, couldn't make the meet. Prado is finishing his senior year at Mission Viejo High School--Barnes' alma mater.

The two former teammates may bump heads against in the 1984 Olympic Games in Los Angeles. Barnes was a consolation finalist at the 1980 Olympic Trials and said he plans to spend next fall training for a shot at the 23rd Olympiad.

But Rio, Barnes said, was not Los Angeles. No score was kept in the meet and he described the competition as "low pressure."

In his spare time, Barnes said he watched the world-famous Rio carnival from free $100 seats, ate dinner with the American consul, and saw the Police in concert.

His only complaint on returning from the equatorial paradise--the water temperature. Barnes said, was "much too hot."