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A grand jury transcript reviewed by a newspaper revealed that New York Yankees slugger Jason Giambi (search) admitted using steroids for at least three seasons, possibly opening him up to punishment by the league and jeopardizing his $120 million contract.

Giambi said he injected himself with human growth hormone in 2003 and used steroids during the 2001-2003 seasons, according to the transcript reviewed by the San Francisco Chronicle.

Giambi's testimony last December, before a federal grand jury investigating illegal steroid distribution, contradicts his public proclamations that he never used performance-enhancing drugs.

Four men, including Barry Bonds' personal trainer, have been indicted in the investigation into the Bay Area Laboratory Co-Operative. The case has cast a cloud of suspicion over home run records set by Bonds and other athletes in recent years.

Giambi was among dozens of elite athletes — including Bonds and track star Marion Jones — who testified before the grand jury last year under a promise of limited immunity from prosecution. Bonds and Jones have denied using steroids.

Giambi's agent, Arn Tellem, didn't return telephone calls seeking comment.

Steroid testing in the major leagues began in 2003, but critics say the penalties are not strong enough. Human growth hormone, or hGH, is not specifically banned by baseball.

Commissioner Bud Selig (search) repeatedly has called for year-round random steroid testing and harsher penalties, but management and the players' union have failed to reach an agreement. The contract runs through the 2006 season.

While discipline is spelled out for positive tests and criminal convictions, admission of steroid use is not addressed. That could give Selig an opening to discipline Giambi.

"I've been saying for many months: I instituted a very, very tough program in the minor leagues on steroids in 2001. We need to have that program at the major league level," Selig said Thursday. "We're going to leave no stone unturned until we have that policy in place by spring training 2005."

Giambi, the 2000 American League MVP with the Oakland A's, signed a seven-year contract with the Yankees before the 2002 season, the sixth-highest deal in baseball history.

Bothered by an injured knee, Giambi hit just .250 in 2003. He batted .208 and played in only 80 games last season, missing time because of a sprained right ankle, fatigue and a benign tumor, which the New York Daily News reported was in his pituitary gland. The Yankees did not even include him on their postseason roster.

Giambi came to spring training this year noticeably trimmer. Asked in February whether he had ever taken performance-enhancing drugs, Giambi said: "Are you talking about steroids? No."

Giambi reportedly testified that one of the drugs he thought he used was Clomid, a female fertility drug that some medical experts say can exacerbate a pituitary tumor.

New York still owes Giambi $82 million, but the Yankees might be able to get out of the deal.

They could argue Giambi's use of steroids violated his contract, allowing them to terminate it or take other action against him.

"We have met with the commissioner's office today and will continue to work with them to obtain all of the facts in this matter," Yankees president Randy Levine said. "We have made no decisions and will keep all of our options open."

Greg Anderson, Bonds' trainer; BALCO (search) founder Victor Conte; BALCO vice president James Valente; and track coach Remi Korchemny have pleaded not guilty to charges that include steroid distribution.

In an interview to be shown on ABC's "20/20" on Friday night, Conte mocked MLB's drug-testing program.

"I think they still believe there's a Santa Claus," he said. "They're not in contact with reality. I mean the program that they put together is a joke."

"Let me tell you the biggest joke of all: I would guesstimate that more than 50 percent of the athletes are taking some form of anabolic steroids," he said.

Conte also said that Jones injected herself in the leg with human growth hormone and was given other performance-enhancing drugs. He said he started supplying Jones with performance-enhancing drugs in the weeks leading up to the 2000 Olympics, where Jones won five medals.

Jones has denied using any performance-enhancing drugs and passed a lie-detector test arranged by her attorneys in June.

"Mr. Conte is simply not credible. We challenge him to submit to the same lie detector procedure that Marion Jones passed," said her attorney, Rich Nichols.