"The revised rule will take effect after a 30-day review by the Environmental Protection Agency, making it one of the last significant changes to environmental regulations by the Bush administration.

"For a quarter of a century, the government has prohibited mining operators from dumping "valley fills," massive piles of debris created by mountaintop removal, within 100 feet of any intermittent or permanent stream if the material harms the stream's water quality or reduces its flow.

"Mining companies have frequently disregarded the law: By the administration's estimate, about 1,600 miles of streams in Appalachia have been wiped out by such activities since the mid-1980s.

"The revised rule calls on companies to avoid the 100-foot stream buffer zone "or show why avoidance is not possible," said a statement from the Office of Surface Mining. If they do dump the waste in the buffer zone, they must try to minimize or avoid harming streams "to the extent practicable."

" 'The agency said the change in regulation would have a "slightly positive' effect on the environment 'because it requires coal mining operations to minimize certain impacts,' but Joan Mulhern, senior legislative counsel for the environmental law firm Earthjustice, called the environmental impact statement "totally inadequate."

" 'It didn't even include the alternative of actually enforcing the rule on the books,' she said. 'The implications of this ruling are devastating, they're widespread and they're irreversible.'

"Before the rule takes effect, Environmental Protection Agency administrator Stephen L. Johnson must certify in writing that the new regulation complies with the Clean Water and Clean Air acts and determine that the environmental impact statement is adequate.

"Mulhern said that she hoped Johnson would block the rule, but if he does not, environmental groups will fight the regulation in court: 'I can't imagine a circumstance in which this is not going to be challenged by environmental groups.' "