The "Superfund" cleanup of toxic waste dumps could eventually cost $11.7 billion in its present form and possibly twice that much, the Environmental Protection Agency has told Congress.

In addition, the EPA said, the eventual cost could be overwhelming if it is forced to expand the fund to cover new threats.

EPA's worst-case "central estimate" of cleanup costs, $22.7 billion, was $6.7 billion higher than the possible upper limit that agency administrator William D. Ruckelshaus gave earlier this year, based on 1,800 to 2,200 cleanups.

The $11.7 billion estimate was for 1,800 cleanups, based on "most likely assumptions and best available estimates." The agency's new low estimate was $7.6 billion.

The agency released a stack of studies nearly three inches thick under the 1980 Superfund law, which required a major report and estimates of future costs by the end of this month.

The law set up a $1.6 billion revolving fund, financed in part by taxes on chemical raw materials, to finance cleanups. That law and its tax expire next September.

In the last congressional session, a renewal bill passed the House but died in the Senate after the Reagan administration argued that Congress should wait for the studies it ordered before making decisions.