The Senate, by a 51-47 margin, defeated a challenge to the Bush administration's strategy on mercury pollution, leaving intact Environmental Protection Agency rules established in March that give power plants flexibility in how they reduce emissions of the dangerous toxin.

Supporters of the repeal argued the strategy was too slow and too weak in dealing with a pollutant that can cause serious neurological damage to newborn and young children. Environmentalists said they would continue to fight the rule via the courts. The EPA has been sued by 15 states and various environmental groups in an effort to reverse the strategy.

The bill, introduced by Sen. Patrick Leahy (D-VT), was co-sponsored by 29 Democrats, Independent James Jeffords of Vermont, and Republicans Olympia Snowe and Susan Collins of Maine. Had the Democrats voted en masse, the bill would have passed. In the final vote, 37 Democrats, nine Republicans and Jeffords voted in favor. Voting against: 46 Republicans and five Democrats. Sens. Orrin Hatch (R-UT) and Jay Rockefeller (D-WV) did not vote.

But, even if the Senate had come through, the White House insisted that President Bush would veto any legislation that overturned the EPA rules.

''In reality this is a political exercise in futility,'' Environment and Public Works Committee Chairman James Inhofe (R-OK) told the Associated Press. ''Who in this chamber would truly believe that the president would sign legislation to repeal his own administration's rule?''

And with that defeatist attitude, Inhofe voted against the legislation.

***

The administration rules, backed by the utility industry, set a cap on mercury emissions. But individual plants, through a cap-and-trade system, can avoid cleanups by buying pollution credits from plants that are under allowable levels.

The rules reversed an EPA position established in 2000 that list electric power plants as a source of toxic mercury and other pollutants subject to the air-toxics provisions of the Clean Air Act. According to those provisions, electric power plants are required to install pollution control equipment that would result in the maximum achievable reduction in toxic mercury and other toxic emissions.