A new crime study shows for the first time which drugs are most prevalent in Prince William County, establishing a way for police to track how much they are used over time.

Marijuana and cocaine are the most-used drugs in Prince William County, while the prescription drug OxyContin does not account for many of the county's drug arrests, according to the report, conducted by the Community Criminal Justice Board, a group of 22 appointed officials that includes police chiefs and judges.

The study, which culled 2003 statistics from county hospitals, schools and police departments and their counterparts in Manassas and Manassas Park, breaks down for the first time arrests by individual drug. Arrests on charges related to marijuana made up 64 percent, or 942, of that year's 1,473 drug arrests, while arrests on charges linked to cocaine and crack made up 17 percent, or 250 drug arrests.

Of the 1,473 drug arrests last year, 1,390 arrests were of adults and the remaining 83 were of juveniles, some of whom were caught with possession of alcohol.

The substance abuse study is significant because it will allow Prince William officials to begin tracking the effectiveness of their drug-enforcement efforts. Maj. Ray Colgan of the Prince William County Police Department said the study provides "a base," and that monitoring the changes throughout the years will be one of the most useful assets in bringing the numbers down.

"This report verifies what we know but we've never had the documentation to back it up," said Christina Frank, the director of the county's Office of Criminal Justice Services, which provides the staff support to the criminal justice board. "I am hoping other localities will do this so we can compare from locality to locality, but right now we're the first. Hopefully, this will spur some of the other localities to follow suit."

Even though no previous studies can be used for comparison at the moment, law enforcement officials charged with analyzing the data say they can nonetheless estimate some patterns based on their experiences on the street.

"We have to see these trends," Colgan said. The study, he noted, showed that 134 drug-related incidents occurred in the school system, but "if we get 640 in two years, we know we have a problem."

Lt. Jay Lanham, a member of the county police department's 30-member vice and narcotics unit, said he believes OxyContin, the prescription pain reliever that has become widely abused in Northern Virginia in recent years, is not as popular as it once was. The study shows that the medication only accounted for 14 arrests, or 1 percent of the drug arrests in 2003.

Since OxyContin began grabbing headlines a few years ago, triggering a nationwide crackdown on abusers and illegal providers, "we saw a decline and [the availability] going down," Lanham said.

Lanham said the dominance of marijuana and cocaine is in line with national statistics, but that other drugs could surface and become popular in Prince William County. The study noted that "street intelligence" indicated that heroin was making a comeback in the area.

Both Lanham and Frank said they were surprised that crystal methamphetamine has not emerged in the county with the same prevalence as elsewhere in the state and country.

"It's really bad in the Midwest, and they have a problem with it in the Shenandoah Valley, but we're not seeing much of it," Lanham said, adding that Prince William police nonetheless busted two crystal meth labs in a home basement and a hotel room recently.

Frank said: "I thought by now it would have made it this way. It's cheap and easy to manufacture."

Of the 134 drug-related incidents that occurred at county schools, Colgan said many students were caught with contraband during one of the police department's monthly drug searches, when officers roam hallways with dogs, or "on Friday night at a football game."