In the 13th major raid this year on illegal PCP laboratories in the metropolitan Washington area, authorities in Virginia have seized what they say was a major source of the drug for Northern Virginia.

Prince William County police, working with state and U.S. drug investigators, arrested three persons who they said were operating one of the largest PCP laboratories ever found in the state.

The raid yielded enough PCP to treat 500 pounds of parsley, the favored ingredient for rolling PCP cigarettes, at a street value of about $100 an ounce, according to Prince William narcotics officer James R. Fry.

The raid occurred Saturday afternoon near an isolated shack on the edge of the Bull Run Mountains in the western part of Prince William County. Fry said the location long has been suspected as a site for the manufacture of the illegal drug, which the federal Drug Enforcement Administration has labeled its "No. 1 priority this year."

Fry said PCP was found "cooking" in several 2 1/2-gallon buckets in the trunks of two rusted cars behind the shack. The chemicals that go into the making in PCP, an animal tranquilizer made from legally obtained ingredients, were discovered in four other old cars on the 15-acre lot, Fry said.

"This bust should lead to a real sharp cut in the supply of PCP in the western end of the county," Fry said. Police said the laboratory was a major source for PCP in Prince William, Fauquier and Fairfax counties.

PCP, known to chemists as Phencyclidine and known on the streets as "angel dust" or when sprayed on parsley as "killer weed," has come into popular use in the nation's high schools in the past three years. The drug causes highly aggressive behaveior and is considered more dangerous than LSD, according to drug enforcement officials.

U.S., state and local efforts to control the availability of the drug in the Washington area this year are starting to show signs of success, according to John A. Meyers, group supervisor of DEA's 10-man PCP task force in the area.

"The purpose of our task force was to knock off the labs," Meyers said yesterday. "The impact of our raids is starting to show up on the street. The price of the drugs is going up and we are getting rumbles that they (prospective manufacturers) are getting paranoid about buying the chemicals (to make PCP)."

Meyers said the 13 raids in the Washington area, which DEA has said is the focal point of a nationwide crackdown on the drug, have recovered PCP and chemical ingredients worth about $4 million on the street.

The arrests over the weekend in Prince William County were made as part of a year-long investigation of PCP sales in Northern Virginia, according to Fry. He said police expect to arrest within the next month as many as 15 others involved in distributing the drug in the area.

Arrested was John W. Rhodes IV, 28, of Haymarket, who was charged with possession and manufacture of PCP and with possession of a concealed weapon. He was released on $6,500 bail. Charged with possession of PCP and marijuana were Eugen T. Tirado, 19, of Manassas, and Mary Jane McDaniel, 19, of Manassas Park.