CONCORD, N.H. – Without debate, the House approved a plan Wednesday to cap emissions from three old fossil fuel-burning power plants.

New Hampshire would be the first state to legislatively regulate emissions of sulfur dioxide, nitrogen oxide and carbon dioxide if the bill becomes law.

Under the bill, Public Service Co. of New Hampshire could clean up the plants or buy credits from utilities that own newer, cleaner plants.

An attempt failed last spring to pass a more stringent bill proposed by Gov. Jeanne Shaheen. This version was put together by environmentalists, the state and the utility.

“I think it’s a very important step on the road to making sure the people of New Hampshire have clean air,” Shaheen said after the vote. “That’s important both for our environment and also for the health of the people of this state.”

No matter what New Hampshire does to clean up its air, the state is susceptible to pollution from Midwest power plants, she said.

Shaheen criticized Congress for not enacting federal pollution controls.

“All of those power plants in the Midwest that we are downwind from were … supposed to have been closed by now,” she said. “But Congress has never been willing to do that so we are still experiencing the pollution from those states.”

The bill involves Public Service’s three fossil fuel-burning plants – in Bow, Portsmouth and Newington – and their emissions of sulfur dioxide, the chief cause of acid rain; nitrogen oxide, which causes smog; carbon dioxide, which affects climate change; and eventually mercury, which threatens the health of humans and wildlife. The plants in Bow and Portsmouth are burning coal; the Newington plant burns natural gas and oil.

The bill sets caps on sulfur dioxide, nitrogen oxide and carbon dioxide emissions that take effect Dec. 31, 2006. A mercury cap would be set later by the Legislature after more tests were conducted on current emission levels.

If Public Service still owns the plants in 2007, complying with the caps would cost about $5 million annually, or about 40 cents per month on an average 500 kilowatt-hour bill.

The bill now goes to the Senate.

Science, Technology and Energy Chairman Jeb Bradley, the bill’s sponsor, has said allowing Public Service to buy credits is essential to keep the plants open and maintain a mix of power sources in the state. If it can’t buy credits, Public Service would need to spend about $160 million to meet the pollution limits, making it cheaper to close the plants and build new natural gas-burning plants.

But Bradley argues New Hampshire should not become too reliant on natural gas. Buying credits from other utilities will encourage them to clean up their plants, he says.

Further, New Hampshire will benefit from cleaner air in upwind states where plants sell credits to Public Service.

Critics like the emission caps, calling them aggressive for regulating carbon dioxide. But they don’t like the credits, which they argue make caps meaningless if Public Service can use them to avoid cleaning up New Hampshire plants.

Credits could be bought from plants that exceed air-quality regulations.

The plan is dividing the environmental community. Some, including the Audubon Society of New Hampshire and the Society for the Preservation of New Hampshire Forests, support it.

Others, including Clean Water Action, New Hampshire Public Interest Research Group and the Sierra Club, oppose the credit trading. They say the three plants are among the dirtiest in the nation and should be cleaned up.