U.S. cyclist Tyler Hamilton could lose his Olympic gold medal and be banned from his sport because of two positive drug tests this summer, Hamilton and Olympic officials confirmed yesterday.

A new testing procedure used for the first time at last month's Olympics detected evidence of blood doping, a banned method of performance enhancement that involves blood transfusions, in tests administered on Hamilton during and after the Games, several officials said.

Hamilton, who won the time trial on Aug. 18, told reporters during a news conference in Regensdorf, Switzerland, that he was "100 percent innocent" and would "fight this until I don't have a Euro left in my pocket."

Confirmation testing on both tests was conducted yesterday, with the results expected in the coming days, officials said.

Hamilton, the first American to win an Olympic road cycling gold medal in 20 years, was told that tests taken on Aug. 19 and Sept. 18 were positive. The first test was administered by the International Olympic Committee a day after his victory in Athens. The second came during the Spanish Vuelta, a popular race in Europe, and was administered by the Union Cycliste Internationale (UCI).

USA Cycling was notified of the IOC test in a letter last Thursday and the UCI test in a separate letter Friday, according to Gerard Bisceglia, USA Cycling's executive director and chief executive.

"It's very early in the process," Bisceglia said. "Because of the impact on the athlete, we take a very strict position on neutrality."

Hamilton faces a possible two-year ban from UCI for one positive test, and as much as a lifetime ban if the UCI were to charge him with two positives. Should the IOC declare him guilty, he would have to relinquish his gold medal and his results would be expunged from the Olympic record.

A record number of athletes -- 24 -- tested positive during the Games and three were forced to give up gold medals. None were Americans.

A spokesperson for the IOC declined to comment.

Like all athletes, Hamilton would have the right to appeal any penalty to the Court of Arbitration for Sport.

Hamilton has ridden in the shadow of Lance Armstrong, but he has earned a reputation as a growing rival and hard-nosed competitor since leaving Armstrong's U.S. Postal team in 2001 to become a featured rider on another team.

Hamilton withdrew from this year's Tour de France after suffering a back injury during the race but finished fourth in the 2003 tour despite riding for three weeks with a broken collarbone. He pulled out of the Vuelta on Sept. 16, complaining of stomach problems.

World Anti-Doping Agency Science Director Olivier Rabin said a test designed to detect blood transfusions was developed over the last three years and finalized this summer by an Australian research group funded by WADA and the U.S. Anti-Doping Agency. The blood test, Rabin said, is modeled on a common paternity test and can detect the presence of blood from another person.

Athletes have long been known to use blood transfusions to enhance their red blood cell count -- and thereby increasing endurance -- in a process known as blood doping. A group of U.S. cyclists was caught blood doping before the 1984 Summer Games in Los Angeles, a bust that led to the banning of the procedure.

Blood doping can be achieved using one's own blood -- frozen months before an event -- or blood from a donor, according to Don Catlin, director of the UCLA Olympic Analytical Laboratory in Los Angeles. Before the institution of the new blood transfusion test, blood doping had been undetectable. However, because the process is complicated and messy, involving wires, needles and bags of blood, Catlin speculated that many athletes turned to injectable blood-boosting drugs such as EPO.

When the IOC began testing for EPO at the 2000 Olympics, Catlin said, athletes might have rediscovered blood doping.

A spokesman for Phonak, Hamilton's team, told the Associated Press that Hamilton did not have a blood transfusion.

"Tyler told us he did nothing," the spokesman, Georges Luechinger, said.

The reputation of Phonak took a hit earlier this summer when rider Oscar Camenzind tested positive for EPO. Camenzind was kicked off the team and announced his retirement.

Cyclist Tyler Hamilton said he is innocent and will "fight this until I don't have a Euro left in my pocket."Tyler Hamilton answers questions about drug tests at a news conference in Switzerland. The American could be banned from cycling for life.