WASHINGTON, Aug. 22 — The Bush administration is set to issue a regulation on Friday that would enshrine the coal mining practice of mountaintop removal. The technique involves blasting off the tops of mountains and dumping the rubble into valleys and streams.

It has been used in Appalachian coal country for 20 years under a cloud of legal and regulatory confusion.

The new rule would allow the practice to continue and expand, providing only that mine operators minimize the debris and cause the least environmental harm, although those terms are not clearly defined and to some extent merely restate existing law.

The Office of Surface Mining in the Interior Department drafted the rule, which will be subject to a 60-day comment period and could be revised, although officials indicated that it was not likely to be changed substantially.

The regulation is the culmination of six and a half years of work by the administration to make it easier for mining companies to dig more coal to meet growing energy demands and reduce dependence on foreign oil.

Government and industry officials say the rules are needed to clarify existing laws, which have been challenged in court and applied unevenly.

A spokesman for the National Mining Association, Luke Popovich, said that unless mine owners were allowed to dump mine waste in streams and valleys it would be impossible to operate in mountainous regions like West Virginia that hold some of the richest low-sulfur coal seams.

All mining generates huge volumes of waste, known as excess spoil or overburden, and it has to go somewhere. For years, it has been trucked away and dumped in remote hollows of Appalachia.

Environmental activists say the rule change will lead to accelerated pillage of vast tracts and the obliteration of hundreds of miles of streams in central Appalachia.

"This is a parting gift to the coal industry from this administration," said Joe Lovett, executive director of the Appalachian Center for the Economy and the Environment in Lewisburg, W.Va. "What is at stake is the future of Appalachia. This is an attempt to make legal what has long been illegal."

Mr. Lovett said his group and allied environmental and community organizations would consider suing to block the new rule.