A 33-year-old man died of an apparent heroin overdose early yesterday, the ninth in an outbreak of heroin-related fatalities in Fairfax County, since May, according to county officials.

Drug deaths, including six in a one-month period, have far outstripped previous records in Fairfax, which authorities say never had more than three fatalities from heroin in any previous year.

Officials believe that the epidemic of overdoses has been caused by unusually potent heroin.

Unusually pure heroin has been blamed for 24 such deaths in the Washington area during August. That figure included an apparently record-breaking 12 deaths from overdoses in the District in the first 17 days of August.

Fairfax County police identified yesterday's apparent heroin victim as John B. Davenport, 33, of 24 Prince Charles Court, Falls Church, whose body was found at 6 a.m. in a parked van in the 4600 block of Hoye Street near the Heritage Mall Shopping Center.

Police said that Davenport and two friends had purchased heroin in the District Friday evening and later injected themselves.

The number of heroin-related deaths has prompted Fairfax County prosecutor Robert F. Horan Jr. to ask county police to "try to find a common denominator among the deaths, a common supplier . . . and see if we might not be able to find out where this stuff is coming from and stop it."

The body of the eighth overdose victim in Fairfax, 31-year-old Angie Sealock, was found Thursday by a friend in her apartment near Alexandria.

Leafing through autopsy reports on seven other people who died of heroin overdoses before Sealock, Horan said that all had needle marks indicating long-term use, which he said suggested that "this is probably bad stuff, as opposed to an explosion of new use."

It's very sad. These are young people," he said. "Unfortunately, this is not a problem people worry about much. "It's the victimless crime syndrome. People figure it's just a bunch of junkies dying anyway.

"But if someone is selling stuff that's making people die, I think society ought to be worried about it. One of these days a young kid taking stuff for the first time is going to get this stuff, and he's going to die for sure."

Five of the nine who died of heroin overdoses in Fairfax were women and four were men.

County police said last week that homicide and narcotics detectives are working together, but so far have concluded only that the heroin is originating outside the county.

Horan said that the suspect heroin is not contaminated, but is simply much more potent than its users are accustomed to. Typically, street heroin ranges from 4 percent to10 percent pure, he said.

"Even users who have developed a tremendous tolerance for the stuff can't handle it" when its purity rises dramatically, Horan said.