The Environmental Protection Agency announced plans yesterday to protect the nation's underground drinking water supply from pesticides by setting limits on their levels in groundwater, restricting their use in areas "vulnerable" to contamination and banning them once they exceed the prescribed limits.

In a proposal open to public review, the EPA unveiled its long-awaited strategy for controlling pesticide pollution of the underground streams that irrigate crops and serve as the source of drinking water for half the American population.

With up to 60 pesticides -- many of them carcinogens -- found in the groundwater of 30 states, the agency has come under increasing pressure to draft a plan. Although there are laws regulating the quality of drinking and surface water and use of pesticides on crops, none comprehensively addresses pesticides in groundwater.

"The actual and potential contamination of our nation's groundwater resources by pesticides poses one of the most critical and difficult environmental concerns of this agency," Assistant EPA Administrator Jack Moore told reporters.

As Moore unveiled the EPA plan, Sen. David F. Durenberger (R-Minn.) introduced legislation calling for more stringent controls in what is expected to be a contentious congressional debate, with environmentalists, farmer interests and the pesticide industry fighting for their causes.

The 150-page EPA proposal is designed to protect current and potential drinking water sources, essentially writing off brackish or nonpotable groundwater.

Brushing aside the goal of "pristine" groundwater as unobtainable, the plan would limit each pesticide to levels as protective of public health as possible given economic and technological constraints. Until a standard is set, carcinogenic pesticides would be restricted to levels of "negligible risk," which means they could not expose people to a risk of cancer higher than one in a million.

As preventive measures, the EPA would establish certain national policies for chemicals known for their penetrating power, limiting their application to certified operators or restricting their use in irrigation waters. Moore said such preventive schemes could be applied to states or regions depending on their soil.

Stricter measures would be applied to such areas as Florida, the Central Valley of California, the southeastern coastal plain and parts of Wisconsin where loose, sandy soils invite pesticide leaching, Moore said.

The EPA blueprint calls for active participation of states to tailor their prevention to local conditions, sizing up soil characteristics and groundwater quality.

Moore called the agency's prevention plan a "yellow light-red light" warning system in which the discovery of pesticides would trigger restrictions. As the levels increase toward unacceptable limits, the regulation would intensify to the point of banning the chemical.

Once levels reached the point of "imminent and substantial endangerment to public health," according to the plan, EPA could order the polluter to provide bottled water.

Different portions of the plan are expected to raise controversy. The pesticide industry worries that state-by-state regulation could lead to 50 different standards.

Environmentalists want protection expanded beyond current and potential sources of drinking water to all groundwater. They want pesticides limited to levels at which they cause adverse health effects instead of economically and technologically feasible levels and stricter enforcement measures.

Durenberger's bill comes closer to the environmentalist demands by setting a goal of "nondegradation" of all groundwater and standards based on health considerations only. His bill would require states to control the sources of groundwater pollution, restricting pesticide application before pollution occurs.