Former Fairfax Board of Supervisors chairman John F. Herrity is having car trouble again.

On Sunday night Herrity was stopped by Fairfax County police and ticketed for making an illegal U-turn on Old Keene Mill Road near Rolling Road, according to a police spokesman. About a week earlier, on Oct. 26, Herrity was ticketed for driving 48 miles an hour in a 35 mile-an-hour zone on Georgetown Pike.

Because of a long history of traffic infractions, the recent tickets may put some sputter in Herrity's revived political career, in which he hopes to get a rematch with Democrat Audrey Moore.

"I know you shouldn't speed and I've been trying like hell not to speed," Herrity said. "I made a mistake."

Herrity said he was not sure if he would contest the tickets, but said that it has been nearly three years since his last speeding violation. He has had one other conviction during that period, which involved an incident in which he struck a bus.

The former chairman is expected to face Supervisor Thomas M. Davis III (R-Mason) in a showdown for the right to run against Moore.

The traffic tickets come at a time when Herrity is trying to make Republicans forget his crushing loss to Moore and persuade them that he can beat her this time around.

During the 1987 race, Herrity's driving record became a major embarrassment and a political liability as the campaign progressed. After four arrests in 15 months in 1986 and 1987, Herrity had a chauffeur drive him to his campaign stops.

Although Herrity declined to say that the recent infractions would harm his chances to beat Davis, he added, "I don't think getting speeding tickets and getting them into the paper is an asset."

Some GOP officials say Davis is their best bet to unseat Democrat Moore, but some have complained that he straddles the fence on issues and is not solidly behind the conservative agenda.

Davis has tried to neutralize that distrust by labeling Herrity as unelectable and portraying himself as the Republican who can unseat Moore, who has been beset by problems during her term.

It could not be learned yesterday how many points Herrity has accumulated against his driver's license, but the former chairman said he has not received a warning letter. Under Virginia law, state officials are not required to divulge the information.

From 1985 to 1987, Herrity was given at least seven tickets, for speeding, running a red light, operation in violation of a restricted license and failing to control his car. He has received at least 20 tickets since he became board chairman in 1976.