Olympic swimming champion Michael Phelps (search) was sentenced to 18 months' probation Wednesday after pleading guilty to drunken driving.

Judge Lloyd O. Whitehead granted Phelps probation before judgment, meaning his record will be expunged if he follows the terms of probation. Phelps pleaded guilty to driving while impaired (search), and prosecutors dropped charges of driving under the influence, underage drinking and failure to stop at a stop sign.

"I recognize the seriousness of this mistake," Phelps told the judge in a packed courtroom. "I've learned from this mistake and will continue learning from this mistake for the rest of my life."

The 19-year-old Phelps was fined $250, must attend a meeting sponsored by Mothers Against Drunk Driving (search), and must give speeches to students at three schools by June 1, advising them about making choices and warning them about the dangers of alcohol.

Whitehead also ordered Phelps to abstain from alcohol and illegal drugs during his probation.

As he left the courthouse, Phelps was besieged by people seeking autographs.

"The past few months have been extremely hard," Phelps said. "I'm looking forward to getting back into the water and getting back to a normal routine."

Under the terms of his probation, Phelps must report to a probation supervisor once a month by telephone or as directed by the court.

"The reason for that is because of his travel," State's Attorney Davis Ruark said.

Normally a probationer would have to report in person.

Phelps, who grew up near Baltimore, recently moved to Michigan. He's scheduled to enroll in January at the University of Michigan, where his longtime coach Bob Bowman is the new men's swimming coach. As a professional, Phelps cannot compete for Michigan.

Phelps won eight medals at the Athens Olympics, including six golds.

Whitehead agreed to go along with the terms of a probation agreement worked out between defense attorneys and the state.

"We learn from our mistakes, and this was a mistake," the judge said after listening to a description of Phelps' accomplishments, background, and community service.

Defense attorney Steve Allen described Phelps as a "remarkably decent young man."

"Michael knows he's a role model and he knows he made a mistake," said Allen, who said Phelps' arrest occurred during "a brief period of decompression after the Olympics."

Phelps was stopped by a state trooper on Nov. 4 for running a stop sign near Salisbury University, about 85 miles southeast of Baltimore.

Phelps was charged with driving under the influence, driving while impaired, violation of a license restriction and failure to obey a stop sign. Maryland's drinking age is 21.

Ruark told the judge that a state trooper stopped Phelps after seeing a car turn right at an intersection in downtown Salisbury without stopping at a stop sign, then abruptly make a left turn onto anther road. Ruark said the trooper detected "an extremely strong odor" of alcohol when he approached the car. And he reported that Phelps' eyes were bloodshot and glassy.

Phelps initially denied drinking, but after performing a variety of field sobriety tests, the trooper advised Phelps that he believed that he had been drinking.

"The defendant responded, 'I know. I'm sorry. I was just scared because I have a lot to lose,"' Ruark said.