A US appeals court unanimously struck down a signature component of President George W.Bush's clean air policies Friday, dealing a blow to environmental groups and likely delaying further action until the next administration takes office in January. The regulation, known 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. "This is 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 court ruled Friday that the EPA overstepped its authority by instituting the rule. It said the Clean Air Act did not give the EPA the authority to change pollution standards the way it did. Citing "more than several fatal flaws," the court 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.