The Senate narrowly turned back a challenge to the Bush administration's strategy on mercury pollution Tuesday, leaving intact federal rules that give power plants flexibility in how they reduce emissions of the dangerous toxin.

With a 51-47 vote, the Senate defeated a resolution to void Environmental Protection Agency rules finalized last March. The Democrats and nine Republicans who supported the repeal contended the EPA approach was too slow and too weak in dealing with a pollutant that can cause serious neurological damage to newborn and young children.

The White House insisted its market-based approach to curtailing mercury pollution is effective and founded on sound science, and warned that President Bush would veto any legislation that overturned the EPA rules.

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

The debate highlighted two very different approaches to environmental protection. The administration rules, backed by the utility industry, would set a nationwide cap on mercury emissions (search) and put a ceiling on allowable pollution for each state. But individual plants, through a cap-and-trade system, can avoid cleanups by buying pollution credits from plants that are under allowable levels.

The utility industry says this method was successful in reducing acid rain in the 1990s.

But opponents say the rules are too weak and would prolong a health risk that leaves newborns vulnerable to birth defects and mental retardation.

The EPA rules, said Sen. James Jeffords, I-Vt., violate the Clean Air Act (search). "The rule is plainly illegal. It is unwise. And it is definitely unhealthy for Americans living downwind of coal-fired power plants, especially mothers and their soon-to-be-born children."

Mercury pollutants work their way up the food chain after being absorbed by fish.

The sponsors of the resolution, Sens. Patrick Leahy, D-Vt., and Susan Collins, R-Maine, turned to a little-used 1996 law that allows Congress to challenge agency rules with a guaranteed floor vote. The law has been successfully invoked only once, when Congress in 2001 repealed Clinton administration workplace ergonomics regulations.

By repealing the EPA rules, the Senate would compel the agency to rewrite the rules. The revisions would be in line with Clean Air Act standards requiring the use of the best available technology to reduce mercury emissions.

Leahy said the Clean Air Act would start reductions in 2008. They would achieve up to 90 percent reductions far sooner than the EPA rules that, according to Leahy, don't begin to cut emissions until 2018 and will not reach the goal of 70 percent reductions until 2030.

But supporters of the EPA rules said repealing the administration approach could have a devastating impact on the economy, forcing power plants to abandon coal for natural gas and driving up natural gas prices. They contended it would cost $358 billion to achieve the 90 percent reduction in three years, as opposed to $2 billion under the administration plan.

"It just can't be justified from a cost-benefit point of view," said Sen. George Voinovich, R-Ohio.

The EPA approach "combines significant reductions in emissions with protection for energy security and consumers," said Scott Segal, director of the Electric Reliability Coordinating Council. "But these senators now seek to disrupt the program."

Opponents of the rule said the cost-benefit argument should factor in a recent study by the Mt. Sinai School of Medicine in New York that the nation loses $2 billion every year from the impact of mercury on child brain development. "I challenge colleagues to tell a whole generation of women and children that their health is less important than energy company profits," Leahy said.