The short-term impact of the rules, the first to limit U.S. carbon emissions from new power stations, is expected to be symbolic -- the rules will not tackle existing plants, which would have been far more disruptive to the industry.
But in the long run it could set the stage for rules that take on such cuts.
"The proposed rule is certainly expected to send the message that coal is dead," said Christine Tezak, an energy policy analyst at wealth management company Robert W. Baird & Co.
Republicans sharply oppose a raft of clean-air initiatives from the EPA and are keen to take the argument on the campaign trail for this year's presidential election that the initiatives kill jobs and saddle businesses with onerous costs.
The longer the administration delays, the less likely the rules will be finalized before November's vote and the greater the chances they could be overturned if President Barack Obama loses.
But EPA chief Lisa Jackson, whose mantra is smart rules can protect the environment, human health and the economy, says the carbon plan will be out early this year.
The delay on the carbon rules is simply to work out the kinks so they are not too costly on power companies, said administration sources, who asked not to be identified.
U.S. states and environmentalists who have sued the EPA in the past to speed up the carbon rules also expect to see the proposal soon. "It's our expectation that the rules for greenhouse gas emissions from new power plants will be issued this month," said Mike Myers, a New York state government lawyer involved in talks with the EPA.