HARRISBURG -- The state Senate approved legislation yesterday that would stop Gov. Ed Rendell from forcing coal-fired power plants to reduce mercury emissions more than federal law requires.

The 40-10 vote sends the bill to an uncertain future in the House, where the chairman of the Environmental Resources and Energy Committee said the measure must force deeper mercury reductions to get out of his committee and get Mr. Rendell's signature.

"We must do better than the federal regulation," said Rep. William F. Adolph Jr., R-Delaware.

The House will be up against a ticking clock: A regulatory review of the Rendell administration's proposed mercury rule is expected to conclude in the fall and does not need approval from the Legislature to become official.

The legislation's passage in the Senate came after months of intense lobbying in the Capitol by the Rendell administration, power companies, business groups and environmental advocates.

Supporters of the legislation said there is no proof that a tougher mercury rule would provide any health benefits. In addition, they said, the cost of complying with Mr. Rendell's proposed rule would force some smaller coal-fired power plants out of business, drive up electricity bills and send power plant jobs to neighboring states.

Opponents said a tougher mercury rule would better protect public health in a state that has the second-highest mercury emissions in the United States and make Pennsylvania a more attractive place for people to visit and live.

Under the federal rule, Pennsylvania is projected to reduce its mercury emissions by 86 percent by approximately 2026, according to the Environmental Protection Agency. The exact year is not clear because power plants can extend the reduction deadline, for instance, by buying "credits" from power plants in other states that have reduced their mercury emissions below required levels.