A federal appeals court unanimously struck down a signature component of President Bush’s clean air policies Friday, dealing a blow to environmental groups and likely delaying further action until the next administration.

The regulation, known as the as the Clean Air Interstate Rule, required 28 mostly Eastern states to reduce smog-forming and soot-producing emissions that can travel long distances in the wind. The Environmental Protection Agency predicted it would prevent about 17,000 premature deaths a year.

Electric power producers challenged the regulation and President Bush found himself with unusual allies.

“This the rare case where environmental groups went to court alongside the Bush administration,” said Frank O’Donnell, president of Clean Air Watch, a group that has criticized other Bush administration policies.

The U.S. Court of Appeals for the District of Columbia Circuit ruled Friday that the EPA overstepped its authority by instituting the rule. The court cited “more than several fatal flaws” and scrapped the entire regulation.

“This is without a doubt the worst news of the year when it comes to air pollution,” O’Donnell said.

The EPA said the rule would dramatically reduce sulfur dioxide and nitrogen oxide emissions, saving up to $100 billion in health benefits. Besides the reduction in premature deaths, the EPA also said the rule would have prevented millions of lost work and school days and tens of thousands of nonfatal heart attacks.

The Bush administration can appeal the decision but environmental groups called for Congress and the EPA to quickly begin working on a new law or replacement regulation.