Officials at Duke Energy don't know how soon they will be able to shut down two coal-burning units at a southern Indiana power plant after deciding to drop a multimillion-dollar project to convert them to natural gas.

The company must reduce air pollution from its four-unit Gallagher plant near New Albany under settlement of a federal lawsuit.

Duke had considered a $71 million project to build a 19-mile gas pipeline that would go underneath the Ohio River to the plant. Duke has now told Indiana regulators it will pay $68 million to buy a greater share of a power plant near Cayuga, about 30 miles north of Terre Haute.

Company spokeswoman Angeline Protogere tells The News and Tribune that some of Duke's 75 employees in New Albany will lose their jobs or be transferred if regulators approve the shutdown plan.

Protogere said Duke hoped for a ruling on its plan so that it could resolve the federal case by mid-November.

"Complying with the agreement we have with the federal government in a way that is most economic with our customers is the overriding consideration in all of this," she said.

Charlotte, N.C.-based Duke agreed in 2009 to spend about $80 million to cut sulfur dioxide emissions at the New Albany plant by nearly 35,000 tons a year.

That was part of the company's $93 million deal with the U.S. Environmental Protection Agency over clean air violations at the plant where unauthorized changes significantly boosted air pollution.

Environmentalists have called the plant, which dates back to 1958, one of the nation's dirtiest in terms of air pollution produced per unit of electricity.

Protogere said Duke officials didn't yet know when the two units at the New Albany plant were expected to be shut down.