Washington Redskins defensive end Dexter K. Manley was arrested yesterday by Fairfax County police on charges of impersonating a police officer and altering the temporary license tags on his Mercedes-Benz automobile, police said.

Manley was represented by his attorney yesterday morning at the county adult detention center where Manley voluntarily reported to police. He posted a $6,000 bond on the felony charge of altering auto license tags and the misdemeanor charge of impersonating a sheriff's deputy, said Fairfax police spokesman Warren Carmichael.

The felony charge carries a penalty of one to five years in jail and up to a $5,000 fine. The misdemeanor charge carries a maximum one-year jail term, a maximum $1,000 fine, or both.

Police stopped Manley, 23, of the 2000 block of Oram Place in Herndon, about 12:40 p.m. Monday, when police officer Michael M. Mack noticed the temporary license tags on Manley's 1981 Mercedes-Benz 450SEL appeared to have been altered by writing in a new date, Carmichael said.

James Kiles, Manley's attorney, said the football player had ordered new auto plates from Texas, where the car was purchased, but that those tags had not yet arrived.

Manley allegedly told police he changed the dates on the tag on the advice of an attorney, police said. Police said that while Officer Mack was questioning Manley on Reston Avenue, he noticed a Fairfax sheriff's deputy's badge pinned inside Manley's wallet. Manley told Mack he was a deputy sheriff, police reports said.

The officer released Manley, then contacted the county sheriff's office and learned the football player had worked as a county deputy during the off-season but had resigned June 13, Carmichael said.

Police telephoned Manley on Monday, ordering him to turn in the badge and accompanying identification card and to appear at the police station yesterday morning. "Manley was somewhat uncooperative," said Carmichael. Police said they then contacted the Redskins management about the incident.

"It is a personal matter of Dexter's and Dexter and his attorneys took care of it," Redskins General Manager Bobby Beathard said yesterday. "We don't plan to take any disciplinary action." Manley, a fifth-round Redskins draft choice from Oklahoma State University, is in his second season with the team.