The Tennessee Valley Authority may not be able to clean up some of its oldest coal-fired power plants fast enough to meet court-ordered pollution controls, agency directors say.

A judicial order to install scrubbers at the John Sevier Fossil Plant near Rogersville, Tenn., by the end of 2011 will be "very difficult, if not impossible" to do on time, TVA Director Howard Thrailkill said.

TVA may appeal the order and could gain more time to continue its pollution controls. A successful appeal also could limit some of the projected $1 billion expense of complying with the order.

The agency's board must decide within six weeks whether to appeal the order, which stemmed from a precedent-setting public nuisance lawsuit brought by North Carolina in 2006.

But with TVA's image already stained this year by its massive ash spill in Kingston, Tenn., critics say an appeal could taint further the utility's environmental record.

"I think an appeal would be tone deaf to what is going on around them and be another black mark for the agency," said Stephen Smith, executive director for the Southern Alliance for Clean Energy.

"TVA has known for years that they need to clean up these plants, but they bet that North Carolina wouldn't win this lawsuit, and they lost and now must pay the price," Mr. Smith said.

In January, U.S. District Court Judge Lacy Thornburg sided with North Carolina's attorney general, who charged that emissions from TVA's coal plants were a public nuisance for the state's residents.

"At a minimum, there is an increased risk of incidences of premature mortality in the general public," Judge Thornburg concluded.

In his 51-page order, the judge said TVA must install scrubbers to limit sulfur dioxide emissions. The agency also must install selective catalytic control devices within four years to cut nitrogen oxides from three coal plants in East Tennessee and one in Northeast Alabama.

TVA said it already planned to put scrubbers on most of the plants. It asked for an extra year to do the work at the John Sevier plant, calling the accelerated timetable a "manifest injustice."

But Judge Thornburg said North Carolina's experts were more convincing than TVA's witnesses in calculating how fast the job could be done.

TVA Chairman Bill Sansom said whatever the utility does now will draw criticism.

"There is a real question about whether we can fit this in this time frame," he said.

Don Barger, southeast regional director for the National Parks Conservation Association, said TVA "can't debate endlessly what it takes to comply with the law."

"There comes a time when we have to do what it takes to have clean air," said Mr. Barger, who testified on behalf of North Carolina in the lawsuit.

phasing out the past

Mr. Barger said Congress adopted clean-air standards for coal plants nearly four decades ago but allowed older plants to operate under less-stringent requirements with the assumption those plants would be phased out in the next decade or two.

But TVA has announced no plans to shut down any coal-fired plants, including some that are now nearly 60 years old.

"We've spent far too much energy on delay and far too little on cleaning up," Mr. Barger said.

Dr. Smith of the clean energy alliance said the North Carolina ruling highlights the need for TVA to begin phasing out its oldest and dirtiest coal plants.

"TVA should have cleaned up these plants years ago, and since they didn't, I think it's time to look at phasing out the oldest and smallest units at plants like Widows Creek in Alabama," he said.

TVA officials insist the federal utility has done more than most other utilities to reduce the emissions from its coal plants. By 2010, TVA will have spent about $5.7 billion on clean-air modifications. It will have cut smog emissions from sulfur dioxide and nitrogen oxide by more than 75 percent since the 1970s, officials said.

Currently, 30 percent of TVA's coal-fired generators have sulfur dioxide scrubbers, compared with just 16 percent at surrounding utilities, agency officials said. More than 60 percent of its coal plants have selective catalytic reduction equipment to control nitrogen oxides. That's more than twice the level at plants owned by neighboring utilities, the officials said.

"We are environmentally sensitive, and we care about the environment," Mr. Sansom said.