Allegheny Energy said the company is taking steps to reduce emissions at its power plants, but estimated it would take roughly $1 billion to achieve total compliance with state and federal regulations, spokesman Allen Staggers said.

The three plants named in the lawsuit are the 1,710-megawatt Hatfield's Ferry plant in Greene County; the 356-megawatt Armstrong plant in Adrian, Armstrong County; and the 420-megawatt Mitchell power plant in Courtney, Washington County. One megawatt powers more than 500 homes.

The state Department of Environmental Protection was joined by attorneys general from Connecticut, Maryland, New Jersey and New York; they contend that prevailing winds carry the harmful emissions that cause smog, acid rain and respiratory diseases.

Allegheny Energy, based in Greensburg, operates 11 coal-fired plants in its system, which provides service to about 1.7 million customers, including about 700,000 in Pennsylvania. The state environmental agency says the company is the fifth-largest emitter of sulfur dioxide and the 10th-largest emitter of nitrogen oxide in the country.

The states' lawsuit seeks to act on a provision of the law called New Source Review, which they say the federal Environmental Protection Agency has failed to enforce under the Bush administration. Under that provision, plant owners are required to install pollution controls when they make improvements that increase output.

The states also allege that EPA data show Allegheny Energy made "major upgrades" to increase generating capacity while failing to install emission controls, according to the 48-page lawsuit filed in Pittsburgh.

Allegheny Energy yesterday said it remains committed to improving environmental performance at its power plants and expressed "disappointment" that the state Department of Environmental Protection felt compelled to challenge the company's operations in Pennsylvania.

"We consider this new action unnecessary, given our pending lawsuit in West Virginia and our plans to reduce the absolute level of emissions at our power plants," said CEO Paul J. Evanson. "We are moving forward as rapidly as our financial condition allows."

Apparently, that is not fast enough for environmental officials.

"We've had discussions with the company. They've been amicable, but the state hasn't been satisfied with their progress. By filing suit, we want to move to a defined, enforceable schedule," said DEP spokesman Kurt M. Knaus.

Allegheny Energy's stock closed yesterday at $25.67, up 37 cents.

Allegheny Energy has been considering the use of "scrubbers" at its Hatfield and Fort Martin power plants, according to Staggers. Scrubbers are any of several forms of chemical devices that remove sulfur compounds formed during coal combustion. He said scrubbers are already in place at the Mitchell power plant.

Staggers also said the company was burning a 25 percent blend of low-sulfur coal from Wyoming's Powder River Basin with high-sulfur Northern Appalachian coal at its Hatfield plant, which the company expects will reduce sulfur dioxide emissions by 25,000 tons annually.

Evanson said the company is working with West Virginia's governor, legislature and various interest groups to finance installation of scrubbers at Fort Martin, and is looking to partner with the same groups in Pennsylvania to make improvements at plants here.

In May 2004, state and environmental officials from Pennsylvania, Connecticut, New Jersey and New York put Allegheny Energy on notice that they were planning to file suit over alleged violations of the Clean Air Act at five coal-fired plants in West Virginia. Plants named in the litigation include the Albright plant at Albright, W.Va., Fort Martin at Maidsville, Harrison power plant at Haywood, Pleasants plant at Willow Island and the Willow Island plant at Willow Island.