Still, Mr. Matheson said, his member co-ops are already moving away from coal in response to economic reality: Other fuels have become more cost-effective. “The electric cooperative fuel mix for providing electricity is changing, with increased investments in natural gas and renewables,” he said.

Indeed, experts said it was unlikely that the new rule would reverse the decline of America’s coal industry. More than 200 coal plants have retired since 2010, mainly because of competition from cheaper natural gas and renewable energy. And dozens of additional retirements have already been announced for the coming years.

At the same time, the new rule is expected to have significant implications for aging coal-fired plants across the country, offering incentives to keep them running longer or enabling them to avoid installing modern pollution controls. The end result, critics of the Trump plan said, would be a rise in not just the heat-trapping gases that are warming the planet but a potential rise in soot and other particulate matter that contribute to health problems such as asthma or pulmonary disease.

“This egregious climate-denial plan fails to protect the American people from the serious risks of climate change,” said Senator Tom Carper of Delaware, the top Democrat on the Senate Environment and Public Works Committee, and “could send clean energy jobs to China.” The plan, he added, “goes even further and allows polluters to increase the amount of smog and soot they emit into the air our children breathe.”

The agency said that the reductions under its proposal would be “comparable” to the Obama rule but “achieved in a legal and reasonable manner.” While the Clean Power Plan aimed to cut carbon emissions 32 percent below 2005 levels by 2030, the Trump plan sets no national benchmark.

By comparison, the Trump plan will cut carbon dioxide emissions from 2005 levels by 0.7 to 1.5 percent by 2030.