WHITE PLAINS, New York (Reuters) - Reversing years of denials, U.S. track superstar Marion Jones pleaded guilty on Friday to lying to federal investigators and admitted using steroids, which could cost her the five medals she won in the 2000 Olympics.

In a sober court hearing and a tear-filled appearance before reporters, Jones, 31, admitted using performance-enhancing drugs.

“It is with a great amount of shame that I stand before you and tell you that I have betrayed your trust,” Jones told reporters outside court, addressing her fans and family.

“I want you to know that I have been dishonest and you have the right to be angry with me,” she said, breaking down in tears. “I have let my country down and I have let myself down.”

The head of the U.S. Olympic Committee urged Jones to give back the medals she won at the Sydney Summer Olympics.

Jones told the court she swallowed tetrahydrogestrinone, or THG, also known as “the clear,” which she said had been given to her by her former coach Trevor Graham.

“I consumed the substance several times before the Sydney Games,” Jones told U.S. District Judge Kenneth Karas in White Plains, just north of New York City. “He (Graham) told me to put it under my tongue and to swallow it.”

She pleaded guilty to two felonies -- lying to federal investigators about her steroid use and lying to them about a separate check fraud case.

Jones faces up to six months in jail under a plea agreement with prosecutors. She was released on bail, surrendered her passport, and will be sentenced on January 11.

She later told reporters she was retiring from track and field, ending a spectacular career in which she became the first woman to win five medals at a single Olympics.

She captured the gold in the 100 meters, 200 meters and 4x400-metre relay, and won the bronze in the long jump and 4x100-metre relay at the 2000 Sydney Games.

USOC Chairman Peter Ueberroth said, “Ms. Jones has cheated her sport, her teammates, her competitors, her country and herself.

“She now has an opportunity to make a very different choice by returning her Olympic medals, and in so doing, properly acknowledge the efforts of the vast majority of athletes who choose to compete clean.”

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The chairman of the World Anti-Doping Agency, Dick Pound, said he expected the IOC to move quickly and strip Jones of her medals.

Jones is already under investigation by the International Olympic Committee for suspicion of using steroids. IOC President Jacques Rogge called it “a sad day for sport.”

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BALCO SCANDAL

Jones became the first athlete convicted in connection with the probe into the San Francisco-area laboratory BALCO, the center of a doping scandal that has tarnished the reputations of leading athletes in baseball, American football and athletics.

In 2004, she told reporters she had “never, never” used performance-enhancing drugs and that “I have accomplished what I have accomplished because of my God-given abilities and hard work.”

In court, she said Graham received “the clear” from BALCO head Victor Conte, one of five men previously convicted for their roles in distributing steroids, including the personal trainer of baseball superstar Barry Bonds.

Jones said she believed at first the substance was flaxseed oil and continued to use it until July 2001, after which she said she realized she was unable to train as intensively and did not recover as quickly afterward.

By November 2003, when interviewed by federal investigators, she knew she had taken THG, but when shown a sample by investigators she said she had never seen it before.

“This was a lie, your honor, as I knew I had taken the substance,” Jones told the judge.

Soon after Jones’ dominating performance in Sydney, her reputation came into question as those around her were ensnared in steroids controversies.

Her then-husband C.J. Hunter, the 1999 world shot put champion, tested positive for steroids in 2000.

Tim Montgomery, former world record holder in the 100 meters and father of one of Jones’ children, was banned for two years by the Court of Arbitration for Sport after evidence showed he had taken THG.

Conte told Reuters that Jones was by no means the only one to blame for her fate.

“Those who have made the majority of the money from Olympic as well as professional sport must also take responsibility for the drug culture that exists,” Conte said.