COLORADO SPRINGS, Colo. — Swimmer Jessica Hardy withdrew from the U.S. Olympic team today, four weeks after testing positive for a banned substance at the national trials.

The U.S. Anti-Doping Agency announced Hardy's decision, saying she did so "in the best interests of the team."

The 21-year-old from Long Beach, Calif., could have contested the drug test results before the American Arbitration Association and potentially filed an appeal with the Court of Arbitration for Sport, which would have kept her Olympic berth in doubt until the eve of the games that open Aug. 8.

Hardy tested positive for a low level of clenbuterol, a prohibited anabolic agent, at the trials on July 4.

A panel from the American Arbitration Association issued a decision Friday that was jointly agreed to by Hardy and USADA after Hardy had a full opportunity to review the laboratory test results and to have those results analyzed by independent experts.

Hardy did not contest the laboratory findings and was granted additional time by the arbitration panel to investigate possible causes of her positive drug test.

The decision allows for a two-year period of ineligibility but allows Hardy to come back to the panel to present evidence that could reduce her period of ineligibility.

"While some might have chosen to exhaust their legal options to try to force their way into the games, Jessica instead chose to put her team's interests ahead of her own," said Travis Tygart, chief executive officer of USADA.

Hardy was tested three times during the trials in Omaha, Neb. The results were negative for the samples taken on July 1, after she won the 100-meter breaststroke, and on July 6, shortly after she claimed another individual spot at the Olympics by finishing second to Dara Torres in the 50 freestyle.

But Hardy's "A'' and backup "B'' samples both came back positive from the test on July 4, when she finished fourth in the 100 freestyle.