In an unusually blunt letter, 11 sponsors of a 1984 crackdown on hazardous-waste disposal accused the Environmental Protection Agency yesterday of ignoring their law and creating more work for itself in an effort to keep landfill sites open.

The letter, signed by a majority of the Senate and House conferees on the legislation, was handed to EPA Administrator Lee M. Thomas at a negotiating session on Superfund.

At issue are regulations the EPA proposed six weeks ago to put the toxic-disposal law into effect. The proposed rules would sanction continued use of landfills, even leaking ones, as long as the dumps pose no more than a minimal threat to health.

Environmental and public-health groups attacked the proposal as running counter to the law, which forbids use of a landfill unless it can be proved that "no migration" of hazardous substances will occur.

EPA officials said they wrote the rules after reviewing congressional intent. But in their letter, the lawmakers told the agency it was all wrong.

"It is hard to imagine how we could have more clearly expressed our intent," they said, contending that the EPA proposal "totally misses the point."

Signed by Senate Environment and Public Works Committee Chairman Robert T. Stafford (R-Vt.), House Energy and Commerce Committee Chairman John D. Dingell (D-Mich.) and nine colleagues, the letter said the EPA has disregarded a "relatively straightforward" law.

The toxic-disposal law "was intended to eliminate land disposal practices that present any threat," the lawmakers wrote. "It was not intended to allow the continued use of land disposal practices that present threats deemed 'acceptable' by the agency on the basis of scientific modeling."

Spokesman Dave Cohen said the agency believes that the proposal "is on solid legal footing" but added that it "will be grappling with many of the concerns raised before a final rule is issued."

The disagreement reflects the debate over EPA reliance on risk assessment in regulating hazards.