WASHINGTON — The Supreme Court agreed Monday to decide how tough the U.S. government can be on 17,000 industrial plants and when it can force improvements in unhealthy air breathed by 160 million Americans.

The closely watched case will test the Bush and Clinton administrations' competing legal approaches for cutting air pollution. Federal appeals courts have issued contradictory rulings on the issue.

The case involves the Bush administration's attempts in 2002 and 2003 to rewrite the Environmental Protection Agency's "new source review" regulations under 1977 amendments to the Clean Air Act.

Those regulations said that older industrial facilities -- such as aging coal-fired power plants, refineries, smelters, and chemical and manufacturing plants -- must install state-of-the-art equipment if they expand or modernize in a way that results in significantly more air pollution.

For more than two decades, the debate has been mired over how to measure pollution and just what constitutes routine repairs, which do not require the best anti-pollution equipment, and facility upgrades, which do.

Regulators, industry groups and environmentalists have their eyes on how the case will affect 600 aging coal-fired power plants, mainly in the East and Midwest, that are among the biggest sources of air pollution.

"It will be pivotal in deciding how the new source review program applies," said Vickie Patton, an attorney for Environmental Defense, which asked the Supreme Court to intervene. "The program has protected millions of Americans from industrial air pollution for a quarter-century."

The 600 generating plants are major sources of nitrogen oxides and sulfur dioxide, which contribute to smog, acid rain, soot and other fine particles that lodge in people's lungs and cause asthma and other respiratory ailments.

In 2004, EPA told 31 governors that areas of their states didn't meet the new federal health standards for smog caused largely by power plants and other industrial facilities, along with cars and trucks. About 160 million people live in those areas.

From the start, the new source review program was criticized as too bureaucratic and complex. In 1999, President Bill Clinton used it to sue owners of 51 aging, coal-burning power plants, primarily in the Ohio Valley and the South.

The Bush administration continued those cases, with some success, while also trying to rewrite the underlying regulations to let more older power plants continue operating without new pollution controls.

One of the Clinton-era enforcement cases, involving Duke Energy Corp. is now before the Supreme Court. The 4th Circuit Court of Appeals ruled last year that power plants can spew more pollutants into the air when they modernize to operate for longer hours.

After Duke won, the Justice Department asked the 4th U.S. Circuit Court of Appeals to reconsider. But the Bush administration then asked the Supreme Court not to overturn the favorable ruling for Duke. Solicitor General Paul Clement explained that Environmental Protection Agency had responded by issuing new regulations.

Source: Associated Press