Florida's U.S. senators were on opposing sides of a debate Tuesday over whether the Bush administration is doing enough to reduce mercury pollution.

In the end, Sen. Mel Martinez won out. The Florida Republican provided a key vote to leave intact Environmental Protection Agency rules that give power plants flexibility in reducing emissions of the toxic pol- lutant.

A resolution supported by Sen. Bill Nelson, D-Fla., to void those rules in favor of more stringent limits was defeated by a 51-47 vote.

"It would have put into place an untested, unrealistic plan," said Ken Lundberg, a spokesman for Martinez.

The current rules have already had a major impact on Gainesville Regional Utilities and its Deerhaven power plant. The utility is planning to spend $90 million upgrading pollution-control systems at the plant, which provides most of Gainesville's electricity.

GRU officials say the upgrade will cut mercury emissions 70 percent by 2010. The current rules push the limits of available technology's ability to reduce mercury emissions, said Ed Regan, the utility's assistant general manager for strategic planning.

"If they made it more stringent I don't know what we would do," he said.

But Holly Binns of the the Florida Public Interest Research Group said Tampa Electric Company and other utilities have shown they can cut mercury emissions by 90 percent at some power plants. She said the EPA rules allow plants such as Deerhaven to take longer to reduce mercury and cut emissions by less than the Clean Air Act mandates.

"EPA's plan is basically too little too late," she said.

But even supporters conceded the vote wouldn't have meant the end of the debate. The resolution would have had to pass the House and overcome a threatened White House veto, both steps that were considered unlikely.

The debate showcased different approaches to environmental protection. The administration rules, backed by the utilities, set a nationwide cap on mercury emissions 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.

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

Mercury pollutants work their way up the food chain after being absorbed by fish. Every inland lake and river in Florida is now under a health advisory because of mercury-contaminated fish.