The so-called "new source review" rules were destined to go into effect Friday. The rules would have allowed companies to conduct repairs or routine maintenance on older facilities without installing expensive pollution-control equipment.

The older facilities were grandfathered in by the 1977 Clean Air Act, under the presumption that they would be taken off line as they became obsolete.

Ruling Wednesday on a challenge brought by 14 states, along with several cities, health and environmental groups, the US Circuit Court of Appeals agreed to block the rules until the legal case can be heard and settled. A final ruling could be nearly a year away.

The states and cities contended that the new rules would harm the environment and lead to more illness and death. The utility industry had argued that the old rules actually led to more pollution because companies were discouraged from making necessary repairs or upgrades to older plants that would improve their efficiency.

The new rules were approved by the Environmental Protection Agency in August.

"The real losers today are American consumers and workers," said Scott Segal, director of the Electricity Reliability Coordinating Council, an industry group made up of large utilities.

"Granting a stay of the equipment-replacement rule is a setback for energy efficiency and environmental protection."

Environmental groups hailed the decision.

The court's ruling "represents a judicial repudiation of the Bush administration's attack on public health protections," said John Walke, director of clean-air programs for the National Resources Defense Council, a party to the suit.

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