For at least six months the FBI has been investigating allegations that longtime Washington County District Attorney John C. Pettit gave preferential treatment to favored defendants and otherwise abused his office.

A half-dozen sources told the Pittsburgh Post-Gazette over the past several weeks that they have been contacted by the FBI about Mr. Pettit's activities. They asked that their names not be made public.

The FBI, following standard practice, would neither confirm nor deny the investigation. FBI investigations do not always result in charges and do not mean that any crime has been committed.

The FBI's questioning appears to be centered on allegations that Mr. Pettit has, as one source put it, provided "special treatment for special people," and that he has given preferential legal treatment to a 30-year-old woman with a record of drugs and prostitution. The FBI is trying to determine if they had a personal relationship.

Mr. Pettit, 70, of Canton, is estranged from his wife. Reached yesterday, he said, "I have no specific knowledge of [an investigation], and I have no further comment about it."

Long a powerful and controversial fixture in Washington County's rough-and-tumble political scene, Mr. Pettit has drawn criticism in recent years for his handling of cases against high-profile defendants and for relying heavily on the testimony of jailhouse informants in homicide cases.

Mr. Pettit made headlines in 2004, the year after winning his sixth consecutive four-year term, when he supported the dismissal of dozens of traffic citations against E. Ronald Salvitti II, the son of a prominent Washington County eye surgeon. The FBI specifically asked about the Salvitti case, according to one source.

The Pennsylvania Department of Transportation had suspended Mr. Salvitti's driver's license for 30 years because of traffic offenses ranging from speeding to driving under a previous license suspension.

When Mr. Salvitti went to court to have dozens of citations overturned so he could regain limited driving privileges, which he said he needed for work and counseling, Mr. Pettit supported the request.

Mr. Pettit said at the time that no special treatment was shown to Mr. Salvitti. He said the justice system sometimes offers a second chance to people trying to turn their lives around.

In 2001, South Strabane police criticized Mr. Pettit for twice dropping cases against private investigator Michael D. Tarbuck, who had been charged with disorderly conduct and assaulting his wife, Mary Lynn. Police, who had answered dozens of calls at the Tarbuck home, said they were angry that Mr. Pettit dropped the charges.

Mr. Pettit defended the decision and said at the time that it could have been overruled by a judge. He said he dropped one of the cases because Mrs. Tarbuck declined to testify.

Mr. Pettit said he knew Mr. Tarbuck personally and professionally, but showed him no special treatment.

Mr. Pettit has built a reputation for building homicide cases on the testimony of prisoners and informants, a practice that led the state Superior Court to order a new trial for one of two men convicted in the 1992 beating death of East Washington insurance adjuster Robert Hannen.

The appellate court overturned the conviction of Lawrence Barnes, citing evidence that one of Mr. Pettit's witnesses was in state prison the night that he said he had observed the defendants in Washington. Mr. Pettit then decided to grant the other defendant, Rodney Yarbor, a new trial.

Rather than risk jury verdicts, the two men accepted plea agreements that kept them in prison about two more years. But they accused Mr. Pettit of prosecutorial misconduct, saying he should have known one of his key witnesses was in prison and could not have seen what he claimed.

Mr. Pettit also had a protracted civil court battle with Frederick Brilla, a convicted drug dealer and one of two men shot dead in a North Strabane tavern in November 2003.

Mr. Brilla sued Mr. Pettit in federal court for refusing to return possessions seized during a pair of drug raids in 1989. A jury held Mr. Pettit personally liable and ordered him to pay $65,000 in punitive damages.

At the time of Mr. Brilla's death, the debt was unpaid. When the county refused to pay the damages for Mr. Pettit, a group of friends donated money to cover the bill.

Three people were arrested for the tavern murders. A jury acquitted one. The other two, who had cooperated with authorities, pleaded guilty to lesser offenses.

The public defender's office criticized Mr. Pettit for meeting with one of the suspects without his attorney present.