The FBI said yesterday that it is investigating allegations that Prince George's County police used excessive force and violated the civil rights of one of its agents during a traffic stop this month.

The agent, Jerry W. Young, who is based in the FBI's Washington field office, has filed complaints that he was unnecessarily handcuffed, pushed to the ground and detained during a traffic stop about 10 p.m. July 19 near Columbia Park Road and East Marlboro Avenue in Landover.

According to written reports of the incident filed by Prince George's police, patrol officer R.A. Hines pulled over Young in his 1986 Chevy Blazer because the agent was towing a trailer without tailights.

At first, Young identified himself as a police officer and said he was unarmed, according to Hines's written report. But after Hines found a .38-caliber handgun in Young's pants pocket, he handcuffed the agent and forced him to the ground, the report states.

After examining Young's credentials, which were in the front seat of his car, Hines and another officer confirmed that they were dealing with an FBI agent and let him go, according to the report.

Angry at the way he had been treated, however, Young drove to the police department's District 3 station in Palmer Park to file a complaint. He told a sergeant on duty that he had been harassed because he was black and had been mistreated. Hines, the officer who pulled Young over, is white.

Peter A. Gulotta Jr., a spokesman for the FBI's Baltimore field office, confirmed yesterday that the agency has opened a civil rights investigation into the traffic stop.

Although he declined to give details, he said the decision to investigate was not based on Young's status as an FBI agent.

Gulotta said the results of the investigation will be forwarded to the U.S. attorney's office in Baltimore and to the Justice Department's Civil Rights Division.

Prince George's police spokesman Royce D. Holloway declined to comment. But John A. Bartlett Jr., president of the Prince George's chapter of the Fraternal Order of Police, said Hines was right to handcuff Young after discovering the gun in his pocket.

"This was an unprofessional agent," Bartlett said of Young. "Not only did he put my officer's life at risk, he put his own life at risk."