Existing rules require US utilities and refineries to invest in state-of-the-art pollution controls if a plant undergoes a major expansion or modification.

But the Bush administration plan proposed last year a change in the definition of "routine maintenance," giving utilities more leeway to modify a plant without triggering extra pollution-reduction requirements.

The EPA said the new rules will give utilities more flexibility to modernize their plants while cutting energy use and pollution emissions.

EPA said it will schedule five public meetings to give critics and supporters a chance to express their views. The agency said it will set meeting locations at a later date.

Democrats and environmentalists call the rule changes a gift to the utility industry and a threat to public health. Emissions from the plants are linked to acid rain, smog and soot, and can aggravate asthma, chronic bronchitis and pneumonia.

Nine Northeastern US states have sued the Bush administration to block the new rules.

"I'd consider (the delay) a minor concession, a part of the administration's effort to soften its image on the environment," said Frank O'Donnell at the Clean Air Trust.

Unless the air pollution rules are eased, aging coal-fired utilities in the Midwest face hundreds of millions of dollars in new investments.

Utility lobbyists approved the delay but called the new rules long overdue.

"It's a reasonable extension but it will not be a massive delay," said Frank Maisano, a spokesman for the Electric Reliability Coordinating Council. "It's a fairly good compromise."