Duke Power wants an exemption from a state air pollution rule as part of its plan to enlarge its Cliffside power plant in western North Carolina.

Officials with the power company, which services much of the state's central and western regions, are asking state lawmakers for a pollution swap: Apply credit for reductions in air pollution gained by a scrubber it's installing at an existing Cliffside unit to offset new emissions from two proposed coal-burning units at the same site.

The trade-off would help the utility avoid a broader review by the U.S. Department of Interior, which operates national parks and wilderness areas and could call for stricter pollution controls on the new units to prevent haze. Duke's Cliffside plant, which is on the border of Cleveland and Rutherford counties, is within range of the Linville Gorge wilderness area and the Great Smoky Mountains National Park.

Environmentalists object to the trade-off, noting that emissions of sulfur dioxide from the coal-burning plant could form haze and reduce scenic views in the tourist destinations.

State rules don't allow utilities to get extra credit for pollution controls installed under the state's Clean Smokestack Act and then use it to offset emissions from new plants. Passed in 2002, the act requires power companies to make significant reductions over the next decade in harmful emissions of sulfur dioxide and nitrogen oxide.

The exemption being considered by legislators is written narrowly to apply only to the Duke plant, but it could set a precedent that other utilities might cite to win similar treatment.

Molly Diggins, of the North Carolina chapter of the Sierra Club, said state environmental regulators passed the rule banning exemptions because they wanted new plants to operate as cleanly as possible and to have the best pollution controls.

She said the exemption would contradict the progressive path North Carolina has been on in recent years to reduce power plant air emissions ahead of federal requirements.

"If you are building this large a facility, it's important to know what the impact is on the Smokies, Linville Gorge and Shining Rock, which are important vacation places for people around the country," Diggins said.

The utility expects the first of two large new coal-burning units with modern pollution controls at Cliffside to go online in 2011. The utility plans to shut down four older power units that do not have pollution controls. Another older unit will be retrofitted with a scrubber that will sharply cut sulfur dioxide pollution.

With the changes they're planning, Duke officials predict that emissions of sulfur dioxide from the Cliffside power plant will drop in 2011 by more than 20,000 tons a year, even as electricity generation triples. But without the exemption, Duke might have to cut emissions even further.

"Don't penalize us just because [the scrubber on the old plant is] paid for by Smokestacks money," said George Everett, director of legislative affairs for Duke Power. "We say that is crazy. We should be praised for the good work we're doing."

If Duke doesn't win the trade-off from legislators, the plant could have to meet tougher pollution limits, said Keith Overcash, director of the state Division of Air Quality.

To do that, Duke officials contend, they would have to cut back electricity production at the new units.