The mining waste rule is enforced by the U.S. Army Corps of Engineers, which has long been criticized by green groups as pro-industry at the expense of the environment.

Lieberman, chairman of the Senate Environment subcommittee that oversees the Clean Water Act, said at a hearing that the new EPA rules violate the act.

The Connecticut Democrat accused the administration of bypassing Congress to weaken federal anti-pollution rules through "administrative fiat." Lieberman said he will introduce legislation to block coal companies from dumping mining waste into waterways.

No Republicans on the subcommittee attended the hearing.

It was unclear whether Lieberman would be able to muster enough support in the Democratic-led Senate or the Republican-controlled House to pass the legislation before Congress adjourns in October.

Environmental issues are expected to figure in many congressional elections in November, which will determine control of both chambers.

Lieberman, who is not up for re-election this autumn, is viewed by many political analysts as a possible presidential candidate in 2004.

Under the new EPA rules, the federal government defines the tons of rubble and rock left from coal mining as "fill material" rather than "waste."

However, the rule change was temporarily halted in May by U.S. Judge Charles Haden, who called it "contrary to the spirit and the letter of the Clean Water Act."

Testifying before the Senate subcommittee, an EPA official said the new rules are needed "to reconcile differing regulatory definitions" between the EPA and the Army Corps of Engineers.

Benjamin Grumbles, an EPA deputy assistant administrator, said the new rules have been "incorrectly painted as being designed to facilitate the continuation of mountaintop mining," and are instead designed "to enhance regulatory clarity."

Mountaintop mining of coal has been an economic boon to poor areas of Kentucky and West Virginia, he said.

The National Mining Association, an industry group, said its studies show 16,000 jobs would be lost over the next five years if companies cannot renew mining permits that allow them to dump the mining waste downhill.

Joan Mulhern, a lawyer at Earthjustice, told the Senate panel the rule change is "one of the most significant and destructive changes to the Clean Water Act protections in decades."