Olympic great Michael Phelps acknowledged "regrettable" behavior and "bad judgment" after a photo in a British newspaper showed him inhaling from a marijuana pipe.

In a statement released Sunday, the swimmer who won a record eight gold medals at the Beijing Games did not dispute the authenticity of the exclusive picture published Saturday by the tabloid News of the World.

"I engaged in behavior which was regrettable and demonstrated bad judgment," Phelps said in the statement released by one of his agents. "I'm 23 years old and despite the successes I've had in the pool, I acted in a youthful and inappropriate way, not in a manner people have come to expect from me. For this, I am sorry. I promise my fans and the public it will not happen again."

News of the World said the picture was taken during a November house party while Phelps was visiting the University of South Carolina. During that trip, he attended one of the school's football games and received a big ovation when introduced to the crowd.

While the newspaper did not specifically allege that Phelps was smoking pot, it did say the pipe is generally used for that purpose and anonymously quoted a partygoer who said the Olympic champion was "out of control from the moment he got there."

The party occurred nearly three months after the Olympics while Phelps was taking a long break from training, and his actions should have no impact on the eight golds he won at Beijing. He has never tested positive for banned substances. The case is unlikely to fall under any doping rules.

Phelps' main sanctions most likely will be financial -- perhaps doled out by embarrassed sponsors who might be reconsidering their dealings with the swimmer.

Phelps was in Tampa, Fla., during Super Bowl week to make promotional appearances on behalf of a sponsor. But he left the city before Sunday's game between the Pittsburgh Steelers and Arizona Cardinals, abandoning his original plan to be at Raymond James Stadium.

The U.S. Olympic Committee said it was "disappointed in the behavior recently exhibited by Michael Phelps," who was selected the group's sportsman of the year. He also was honored as AP male athlete of the year, and his feat in Beijing -- breaking Mark Spitz's 36-year-old record for most gold medals in an Olympics -- was chosen as the top story of 2008.

"Michael is a role model, and he is well aware of the responsibilities and accountability that come with setting a positive example for others, particularly young people," the USOC said in a statement. "In this instance, regrettably, he failed to fulfill those responsibilities."

USA Swimming said its Olympic champions are "looked up to by people of all ages, especially young athletes who have their own aspirations and dreams."

"That said," the governing body added, "we realize that none among us is perfect. We hope that Michael can learn from this incident and move forward in a positive way."

Phelps was part of a group of elite athletes who agreed to take part in a pilot testing program designed to increase the accuracy of doping tests. His spot in the program could be at risk, said Travis Tygart, head of the U.S. Anti-Doping Agency.

"For one of the Olympics' biggest heroes it's disappointing, and we'll evaluate whether he remains in that program," Tygart said. "But some good education comes from this because he's going to suffer some penalties."

Marijuana is viewed differently from performance-enhancing drugs, according to David Howman, executive director of the World Anti-Doping Agency. An athlete is subject to WADA sanctions only for a positive test that occurs during competition periods.

"We don't have any jurisdiction," Howman said. "It's not banned out of competition. It's only if you test positive in competition."

Phelps returned to the pool a couple of weeks ago to begin preparations for this summer's world championships in Rome. He plans to take part in his first post-Olympics meet in early March, a Grand Prix event in Austin, Texas.

This isn't the first embarrassing episode for Phelps after an Olympic triumph. In 2004, a few months removed from winning six gold and two bronze medals in Athens, the swimmer was arrested on a drunken driving charge at age 19. He pleaded guilty and apologized for the mistake.

In his book "No Limits: The Will to Succeed," Phelps recounted how his first phone call was to his agent, and not his mother or coach Bob Bowman, because he knew they would yell at him.

Later, he called Bowman, who was supportive but told him, "Michael, just because you want to blow off some steam doesn't mean you can be an idiot."

Debbie Phelps, his mother, cried at the news of the drunken driving charge.

"That hurt worse, maybe, than anything," Phelps wrote