A U.S. weightlifting titlist yesterday challenged statements by the executive director of the U.S. Olympic Committee, who said that some U.S. and foreign athletes had deliberately performed poorly in their events in the Pan American Games last month to avoid being tested for performance-enhancing drugs.

"How can you make a statement like that without being able to prove it?" said Michael Cohen of Savannah, Ga., who won a silver medal in the snatch at Caracas. "An athlete is affected by his environment, and the environment at the Pan American Games was atrocious. There was no air conditioning and the window in my room had no screen on it."

In Mexico City, Mario Vasques, the president of the Pan American Sports Organization, acknowledged that in Caracas last month, "There were many rumors that the athletes were throwing the games. I suppose it could be true, but I don't believe it. Athletes want to compete. They aren't going to throw a game because of the tests."

On Tuesday, Col. F. Don Miller, executive director of the USOC, said some of the athletes at the Pan American Games "had thrown their contests so they would not be tested" for the banned substances. Miller declined to say how many or name the athletes but said, "I know very well what happened in my own heart."

Yesterday William E. Simon, president of the U.S. Olympic Committee, supported Miller's observations. "Don kind of said it all," said Simon. "Don and I had talked about the athletes' underperforming. You don't want to suffer the stigma of going home and you don't want to get tested so you underperform."

A controversial issue in international sports for two decades, the use of drugs by athletes to enhance their performance became a major controversy at the Pan American Games when 17 athletes were stripped of medals and records after they tested positively for substances banned by the International Olympic Committee. Additionally, 12 U.S. athletes withdrew from competition and went home, presumably rather than undergo new and sophisticated drug screening procedures used at the games.

Drug screening procedures varied from sport to sport at the Pan American Games, but in most cases athletes who won medals could count on being tested.

John Randolph, the coach of the U.S. track and field team at the Pan American Games, had several of his athletes withdraw from competition and go home rather than be tested. "Anything that I am involved in, if you put a U.S. suit on your back, you are going to compete to the best of your ability," he said.

That his own athletes did their best, "is beyond refute," said Randolph, who also observed that "there were some strange things that happened at those games . . . The thing had to surface, and I'm glad that it did. Hopefully there will be some stringent reforms."

Cohen, who moved up a notch in weight class this year and won a national title in the 198-pound division, said the atmosphere in Venezuela was less than conducive to exemplary athletic performance.

"We were 25 miles from Caracas, and the place we stayed had two toilets for nine athletes, and they were always stopped up. And there was no hot water.

"Most American athletes are not used to staying up until 3 o'clock in the morning, but I could not close the window in my room and at 2 o'clock in the morning there were people outside my window shouting and yelling and going ape."

Cohen also said many athletes fear the IOC's list of banned substances is so inclusive that normal medications will cause an athlete to risk disqualification. "I'm competing in an international weightlifting match in Russia next month. I've got a case of the sniffles, but I'm afraid to take a decongestant," he said.

In Colorado Springs yesterday, the USOC confirmed that a second U.S. gold medalist at the Pan American Games, sombo wrestler Rebecca Scott of Kansas City, had been stripped of her title after testing positive for a banned substance, testosterone. Weightlifter Jeff Michels of Chicago was stripped of three medals at the games after testing positive for testosterone, but Scott did not compete until the next-to-last day of competition and the tests were not finished until after the games were over and all the athletes had returned home.

Scott, however, has denied any illegal use of testosterone, contending any traces of the substance are the result of birth contol pills.

Roy Bergman, chief physician for the U.S. team at the games, said he had spoken with the manufacturer of the pills, which do contain testosterone. The manufacturer said it was possible the pills could have caused Scott's tests to register a false positive, Bergman said, and Scott will probably be retested.