WHITE PLAINS, N.Y. — For years, Marion Jones angrily denied using steroids. Today, she admitted it was all a lie.

The three-time Olympic gold medalist pleaded guilty to lying to federal investigators when she denied using performance-enhancing drugs. She also pleaded guilty to a second count of lying to investigators about her association with a check-fraud scheme.

Seated at the defense table and speaking in a clear voice through a microphone, Ms. Jones admitted to doping and said she lied about it to investigators in 2003.

She said she was told by her then-coach Trevor Graham that she was taking flaxseed oil when it was actually steroids.

“By November 2003, I realized he was giving me performance-enhancing drugs,” she told the judge.

Ms. Jones was released on her own recognizance and was due back in court January 11 for sentencing.

It was a stunning fall from grace for Ms. Jones, once the most celebrated female athlete in the world. She captivated the country with the audacious goal of winning five gold medals at the Sydney Olympics. Though she fell short — three golds but two bronzes — her charm and winsome smile made her a star.

Seven years later, she is broke, her reputation is ruined, and she is looking at prison time. And she will likely lose those five medals she won in 2000.

Dressed in a dark suit and pink shirt, Ms. Jones was somber when she arrived at U.S. District Court in Westchester County with her mother and her attorney, biting her lower lip as reporters and cameras swarmed her. Her mother stumbled at one point but got up and accompanied her daughter inside, where she was fingerprinted and booked before the hearing.

The flaxseed oil Ms. Jones said was given to her actually was “the clear” — a performance-enhancing drug linked to BALCO, the lab at the center of the steroids scandal in professional sports. Home run king Barry Bonds of the San Francisco Giants also has been linked to the Bay Area Laboratory Co-Operative, and was one of more than two dozen athletes who testified before a federal grand jury in 2003.

Mr. Bonds denied ever knowingly taking performance-enhancing drugs, saying he believed a clear substance and a cream, given to him by his trainer, were flaxseed oil and an arthritis balm.

The International Olympic Committee already has opened an investigation into doping allegations against Ms. Jones in December 2004, and said today it will step up its probe and move quickly to strip her of her medals.

Under statute of limitations rules, the IOC and other sports bodies can go back eight years to strip medals and nullify results. In Ms. Jones’ case, that would include the 2000 Olympics, where she won gold in the 100 meters, 200 meters and 1,600-meter relay and bronze in the long jump and 400-meter relay.

In addition to any jail term, Ms. Jones could face a long competition ban.