The Fairfax County Board of Supervisors asked the Virginia General Assembly yesterday to prohibit uranium mining in the state until the potential environmental dangers can be assessed.

Board Chairman John F. Herrity, whose resolution was unanimously endorsed by the nine-member board, said he feared mining and processing of radioactive uranium in Prince William County might pollute the Occoquan River, which supplies drinking water to Alexandria and much of Fairfax and Prince William counties.

The Marline Uranium Corp. and other, unidentified mining firms are seeking mining rights in Prince William, Fauquier, Culpeper and other Virginia counties. Herrity said mines in Northern Virginia would be the first east of the Mississippi and the first in such densely populated territory.

"There are big bucks in this," a Herrity aide said. "I think they should just calm down and take a look at it."

Ed Lane, a former Richmond legislator and a lobbyist for Marline, a subsidiary of Marline Oil Corp., recently circulated proposed legislation to General Assembly members, bypassing a subcommittee of the Virginia Coal and Energy Commission that has been studying the uranium issue. Some local officials in Virginia say the Marline proposal would eliminate local control over uranium mining.

The Orange County Board of Supervisors and the Fredericksburg City Council have already urged that Virginia enact a moratorium similar to ones in New Jersey and Vermont. The Fairfax board urged that the moratorium last as long as it takes to study potential dangers and establish safeguards.

"This could be the first evidence of something more broad that could affect people in this area substantially," said Supervisor Audrey Moore of Annandale. She urged Alexandria and Prince William to follow the Fairfax move.