Eighty-six U.S. athletes, including two who already had made the 1984 Summer Olympic team, flunked drug tests in the nine months preceding the Los Angeles Games, the U.S. Olympic Committee reported yesterday.

Ten of the athletes who failed were screened during the Olympic trials, including the two who already were on the U.S. team when their drug tests came back positive, USOC officials reported. The tests found evidence of stimulants, anabolic steroids or testosterone in the athletes' bloodstreams.

The two athletes who failed were removed from the Olympic team and replaced by alternates. Their names remain confidential, although USOC spokesman Mike Moran said yesterday, "It did not involve big-name athletes." None of the other 84 participated in the Olympics.

A total of 2,254 U.S. athletes was tested by the USOC's Drug Control Task Force before final Olympic team selections were made. The USOC said 33 athletes tested positive for use of stimulants and another 53 for use of anabolic steroids or testosterone, which also is a steroid.

This is the second controversial medical story to hit the USOC this week. Danny Van Huarte, a member of the U.S. Olympic cycling team, admitted on the "CBS Morning News" yesterday that, during the Olympics, he underwent blood doping, in which an athlete receives blood tranfusions to increase the volume of red blood cells, which carry oxygen to the muscles. This is widely believed to enhance endurance.

Van Huarte's admission follows a Rolling Stone article, set for a Jan. 29 release, reporting that about one-third of the cycling team, including medal-winners Steve Hegg, Rebecca Twigg, Brent Emery, and Leonard Nitz, received transfusions before their events in direct violation of USOC policy.

Executive Director F. Don Miller, speaking at a news conference in Indianapolis yesterday, said the USOC has confirmed blood doping in Los Angeles, and added the athletes would be "held accountable." Moran said any doctors involved in the blood doping were not members of the USOC delegation, but would be under the review of the Bureau of Quality Medical Assurance of the state medical licensing board of California.

Dr. Irving Dardik, head of the USOC's panel investigating the blood doping, said that "a handful" of cyclists, along with their coaches and doctors, also experimented with caffeine before racing.

"The same individuals also were looking at caffeine to improve performance," he said. The USOC is investigating.

Following the release of the USOC's drug testing report, Miller said the task force was a success because no U.S. athlete failed drug testing during the Winter or Summer Olympics.

The USOC established the task force in 1983 after the Pan American Games, in which two U.S. athletes were disqualified after testing positive for use of anabolic steroids or testosterone.

Some of the pre-Olympic tests were done informally, meaning the athletes did not face penalties if evidence of drug use was found. Miller, who is leaving his USOC job next month, said he will recommend that all tests be done formally.

"This means that the testing will be done with the knowledge by the athlete that positive tests will result in penalties," Miller said. "Our athletes have had over a year of education and information in this process and an awareness of our firm position against the use of drugs."

Informal testing gives athletes who are using drugs time to stop before formal tests begin. Miller said a few athletes were able to escape detection as a result.