Pennsylvania on Thursday will begin enforcing a federal clean-air rule to reduce emissions of smog-forming pollutants from power plants following a court decision that affects 28 states including New Jersey, officials said yesterday.

The rule, which required states mostly in the East to cut emissions that are carried long distances by wind, was thrown out in July by the U.S. Appeals Court for the District of Columbia.

Last Tuesday, a three-judge panel of the same court temporarily reinstated the rule until the U.S. Environmental Protection Agency develops a new program.

Judge Judith W. Rogers said in the panel's opinion that allowing the country to go without the protection of the Clean Air Interstate Rule, known as CAIR, while the EPA fixes it "would sacrifice clear benefits to public health and the environment."

The judges did not give EPA a deadline to come up with new regulations, but warned that their decision was not an "indefinite stay" of the July ruling.

Meanwhile, Pennsylvania will begin enforcement on Thursday, the state Department of Environmental Protection said yesterday.

John Hanger, acting secretary of the department, said in a statement that workers were moving forward "with our state implementation plans to meet ozone and fine-particulate standards and to improve visibility while reducing regional haze."

Pennsylvania is among the nation's top producers of nitrogen oxides and sulfur dioxide because it has so many coal-fired power plants.

The pollutants contribute to smog, which can cause or exacerbate asthma, bronchitis and other breathing problems.

A representative of the state's power plant owners said they already have spent more than $4 billion at 30-plus coal-fired power plants to comply with the rule.

In the Philadelphia region and throughout New Jersey, where there are fewer plants, a chief concern has been pollution blowing in from plants to the west.

Both states are members of the Ozone Transport Commission, which was established to address the transport of ground-level ozone and the chemicals that contribute to its formation - oxides of nitrogen and volatile organic compounds.

The commission has announced a cooperative effort among the states to develop a multi-pollutant strategy to meet the ozone standard.

"New Jersey is committed to that effort," said DEP spokeswoman Elaine Makatura, a spokeswoman for the New Jersey Department of Environmental Protection. She could not say yesterday whether the state would, like Pennsylvania, immediately begin enforcing the rule.

Environmentalists applauded last week's court decision reinstating the rule, one of the few environmental actions by the Bush administration that they supported.

The EPA has predicted that the new regulation would prevent about 17,000 premature deaths a year and would save up to $100 billion in health benefits, eliminate millions of lost work and school days and prevent tens of thousands of heart attacks.