Mining companies remove vast surface areas to expose the coal in a procedure known as mountaintop removal. The process often involves dumping the dislodged dirt and rock into valleys.

Environmentalists estimate hundreds of miles of streams have been affected, some of them obliterated, because of lax enforcement of the 1983 restrictions or different interpretations of the federal rule.

"Kentucky's vast water resources are critical to our health and economic development, and I do not believe the newly proposed waivers can be effectively and uniformly applied to protect these water resources,'' Beshear wrote.

Conway said he realizes coal is an integral part of Kentucky's economy and an important energy resource.

"Nevertheless, our rivers and streams are also critical natural resources that must be protected if we are to pass along a stable environment to coming generations,'' he said.

Conway, Kentucky's top prosecutor, said he believes the proposal has "the potential to open up increased environmental abuse'' in the state.

Beshear said the proposal would threaten Kentucky's ability to protect its environment.

The Bush administration has advanced a proposal that would ease restrictions on dumping mountaintop mining waste near rivers and streams, eliminating protections that have been in place for a quarter-century.

The Office of Surface Mining issued a final environmental impact analysis last month on the proposed change that has been under consideration for four years. The modification has been a top priority of coal operators who want to see it implemented before the Bush administration ends.

The proposal would rewrite a regulation enacted in 1983 by the Reagan administration that bars mining companies from filling Appalachian valleys with dirt and rock blasted from mountaintops in the removal of coal. The regulation prohibits mining activities within 100 feet of any intermittent or perennial stream if the disposal adversely affects water quality or quantity.

The revisions would let mining companies skirt the 100-foot protective buffer zone if compliance is determined to be impossible, but would require mining companies to minimize the environmental impact.

Beshear publicly released his letter objecting to the change on Tuesday. In it, he said the proposed change "leaves open increased opportunities for abuse'' by mining companies.

Other Kentucky political leaders, including U.S. Reps. Ben Chandler and John Yarmuth and Attorney General Jack Conway, wrote similar letters. All called for rejection of the proposal.

Mining companies remove vast surface areas to expose the coal in a procedure known as mountaintop removal. The process often involves dumping the dislodged dirt and rock into valleys.

Environmentalists estimate hundreds of miles of streams have been affected, some of them obliterated, because of lax enforcement of the 1983 restrictions or different interpretations of the federal rule.

"Kentucky's vast water resources are critical to our health and economic development, and I do not believe the newly proposed waivers can be effectively and uniformly applied to protect these water resources,'' Beshear wrote.

Conway said he realizes coal is an integral part of Kentucky's economy and an important energy resource.

"Nevertheless, our rivers and streams are also critical natural resources that must be protected if we are to pass along a stable environment to coming generations,'' he said.

Conway, Kentucky's top prosecutor, said he believes the proposal has "the potential to open up increased environmental abuse'' in the state.