One of the nation's largest power generators has agreed to end a years-long federal lawsuit by paying $4.6 billion to reduce pollution that has eaten away at Northeast mountain ranges and national landmarks, The Associated Press has learned.

The settlement requires American Electric Power, based in Columbus, Ohio, to reduce chemical emissions that cause acid rain by at least 69 percent over the next decade.

It also fines AEP an additional $15 million in civil penalties and another $60 million in cleanup and mitigation costs to help heal parkland and waterways that have been hurt by the pollution.

Details of the agreement were provided by two people familiar with its terms who spoke on condition of anonymity Monday because it had not yet been filed in federal court. Spokesmen for AEP declined comment Monday.

The settlement marks one of the largest government fines in an environmental case. Exxon Mobil Corp. estimates it has paid $3.5 billion in cleanup costs, government settlements, fines and compensation for the 1989 Exxon Valdez oil spill. The company is fighting an additional $2.5 billion in punitive fines.

Nine states, a dozen environmental groups and the Environmental Protection Agency brought the lawsuit against AEP in 1999, accusing the energy company of rebuilding coal-fired power plants without installing pollution controls as required under the Clean Air Act.

Increased acid rain problems in the Northeast over the last quarter-century have been linked to sulfates and nitrates, which are products of coal-fired power plants. Landmarks like the Statue of Liberty and the Adirondacks mountain range in upstate New York have been irreparably damaged by acid rain, environmentalists say.