The Environmental Protection Agency filed a civil lawsuit yesterday against the Occoquan sewage treatment plant serving Fairfax County, Manassas and Prince William County, claiming it illegally permits industries to dump untreated toxic wastes into its sewage system.

The treatment plant, located in Centreville, is not equipped to treat toxic wastes, according to EPA attorney Bruce C. Buckheit. But for more than two years, the Upper Occoquan Sewage Authority has allowed industries to dump contaminated materials into the sewage system without requiring them to pretreat it, he said.

"We are not alleging specific health hazards now, but the idea is to prevent them," said Buckheit. "That water goes on to the Occoquan Reservoir, which people in Fairfax and Alexandria drink from ."

Millard Robbins, executive director of the Occoquan plant, denied the EPA's charges. "We have one of the most sophisticated plants in the country," he said. "And our industries do pretreat their wastes."

In the lawsuit filed in U.S. District Court in Alexandria, the EPA is asking the court to levy "such relief as necessary," up to the maximum penalty of $10,000 a day dating from July 1, 1983, when federal law required Occoquan to ensure that industries were pretreating wastes dumped into its sewage system.

The Upper Occoquan Sewage Authority, regulated under the state of Virginia, treats more than 5 million gallons of raw sewage daily, much of which then flows to the Potomac River Basin.