The Obama administration took its strongest action to date against highly destructive mining practice today, putting a hold on dozens of mountaintop removal projects in the Appalachian region.

The Environmental Protection Agency said it was ordering a review of 79 permits in West Virginia, Virginia, Ohio and Kentucky to mine for coal by blowing the tops of mountains to assess the impact on water quality.

Mountaintop removal involves dynamiting the tops of mountains - leaving mounds of debris in neighbour rivers and waterways - razing forests and cutting off hundreds of feet of rock to reach narrow seams of coal.

The EPA said it had continuing concerns about toxic debris from the mine sites, and the loss of hundreds of miles of streams, which were choked off by the rubble.

"The administration pledged earlier this year to improve review of mining projects that risked harming water quality. Release of this preliminary list is the first step in a process to assure that the environmental concerns raised by the 79 permit applications are addressed and that permits issued are protective of water quality and affected ecosystems," the EPA administrator, Lisa Jackson, said in a statement.

The decision was welcomed by some environmental organisations as a key break by the Obama administration with the policies set by George Bush.

Appalachian Voices, a local activist coalition, said in a statement:

"By recommending these permits not be approved, the EPA and the Army Corps has demonstrated their intention to fulfill a promise to provide science-based oversight which will limit the devastating environmental impacts of mountaintop removal mining."

But environmental organisations are still pressing the Obama administration for an outright ban on mountaintop removal, which environmentalists say is the most destructive method of extracting coal.

Bush-era regulations had made it far easier for mining companies to win approval for mountaintop removal and to avoid regulatory control. The EPA, in Bush's eight-year term, did not oppose a single permit for mountaintop removal.

Jackson, in a recent interview, admitted the agency had grown "toothless".

The Obama administration signalled last June that it would take a tougher approach to enforcement. Earlier this week, the agency said it would halt West Virginia's biggest mining project, spread over 2,300 acres, because of concerns over dumping debris.

The agency now has two weeks to issue its final decision on the pending permits. Projects that do meet EPA environmental standards will move ahead.