Coal accounts for more than half the electricity produced in the United States, but emissions of mercury, sulfur dioxide and other pollutants draw fire from environmentalists.

There is, however, growing interest in "clean coal" technologies to reduce emissions from power production.

Sempra Generation, a unit of San Diego-based Sempra Energy, is proposing a 600-megawatt, coal-fired plant in south-central Idaho near Jerome to sell electricity to customers in the Pacific Northwest, Utah and Nevada.

Southeast Idaho Energy LLC plans a 520-megawatt coal gasification plant in Pocatello.

Electricity demand in Idaho is growing by an estimated 50 megawatts a year, or enough power for about 40,000 US homes, said Jeff Beaman, spokesman for Idaho Power, the state's largest utility and a unit of Idacorp .

Long-range energy planning also is underway in California, Arizona, Nevada, Utah, Wyoming and other states to develop new coal-fired plants, wind power farms and transmission lines to deliver electricity to the region beginning about 2012.

Idaho is among a handful of states with no coal-fired plants. Under new federal air quality standards, the state is set at a zero cap on mercury emissions from power plants, making it virtually impossible for coal-fired facilities to operate.

MERCURY EMISSIONS

But a proposed rule change by the Idaho Department of Environmental Quality (DEQ) would make the state eligible for mercury emissions from coal plants under a federal emissions cap-and-trade program.

The program allows energy companies nationwide to sell the unused portion of their pollution caps to competitors.

The program's goal is to reduce emissions of mercury, which has been linked to brain damage in fetuses and children.

"Decreasing emissions across the United States do not mean you won't have local hotspots," said Martin Bauer, director of DEQ's Air Quality Program. "What you're taking away from a Virginia or a Pennsylvania you may end up increasing in Idaho."

Idaho residents have until Wednesday to weigh in on the matter before the DEQ.

Sempra has been the target of mounting opposition in Jerome, a farm town connected by rail to the coal fields in Wyoming's Powder River Basin.

"The citizens of Idaho don't deserve to breathe in all the pollution pumped into the air from the plant to make power for other people." Lauren McLean, a spokeswoman for the Idaho Conservation League spokeswoman said.

Sempra officials say the plant will be an economic boon to the area, contributing an estimated $18 million in tax revenues a year. The company has pledged to take advantage of coal plant technology that reduces emissions by 10 percent and boosts plant efficiency.