At least 50 hazardous-waste disposal sites have shut down rather than comply with new federal regulations on toxic waste disposal, taking advantage of what an environmental group has called an "escape window" that may let polluters avoid the expense of cleaning up their own messes.

The Environmental Protection Agency's final rules under the Resource Conservation and Recovery Act, the 1976 law governing hazardous-waste disposal facilities, stipulated that any facility closed by Jan. 26, 1983, would not fall under the rules that hold the owners and operators strictly responsible for contamination.

An EPA list of the sites that took that option, released by the Environmental Defense Fund, includes sites operated by such large corporations as Bethlehem Steel (in New York and Washington), Union Carbide (in West Virginia and South Carolina), Hooker Chemicals and Plastics (Michigan) and Texaco (Wyoming).

The environmental group said the EPA does not know how many facilities closed part of the site and left other parts open. "You'd have to be crazy not to shut down those portions of a facility causing a problem," said Linda Greer, an EDF scientist.

EPA officials responded that the option was included in the rules because the law required it; they contended that the EPA still will have the authority to protect public health at the facilities.