Silhouetted against the sky at dusk, emissions spew from the smokestacks at Westar Energy's Jeffrey Energy Center coal-fired power plant near St. Mary's, Kan. (Charlie Riedel/AP)

The Obama administration is leaning toward revising its landmark proposal to regulate greenhouse gas emissions from new power plants, according to several individuals briefed on the matter, a move that would delay tougher restrictions and could anger many environmentalists.

The discussions center on the first-ever greenhouse gas regulations for power plants, which were proposed by the Environmental Protection Agency nearly a year ago. Rewriting the proposal would significantly delay any action, and might allow the agency to set a separate standard for coal-fired power plants, which are roughly twice as polluting as those fueled by natural gas.

While the move could bolster the administration’s legal justification for regulating power plants’ carbon emissions, any delay on the rules would be a blow to environmental groups and their supporters, who constituted a crucial voting block for President Obama and other Democrats in last year’s elections.

Individuals familiar with the matter asked not to be identified because a final decision has not been made. The White House declined to comment.

Obama, who is visiting Argonne National Laboratory outside Chicago on Friday to tout his clean-energy agenda, has vowed to fight global warming by using his executive authority since congressional Republicans have blocked climate-change legislation. Regulating utilities represents the best opportunity for the president to cut the nation’s carbon output.

Last year, the EPA proposed the first-ever greenhouse gas standard for new power plants, which would require any new power plant to emit no more than 1,000 pounds of carbon dioxide per megawatt hour of electricity produced. The agency is supposed to finalize the rule by April 13 but is likely to miss that deadline, and officials are discussing with the White House how they might modify the proposal in order to ensure it can survive a legal challenge.

Environmentalists are particularly worried about finishing the standards for new power plants because they are less controversial than imposing carbon limits on the existing plants that emit 2.2 billion tons of carbon dioxide a year, or 40 percent of the nation’s carbon output. The Obama administration has yet to say if it will pursue that policy.

David Doniger, a senior attorney at the Natural Resources Defense Council and director of the group’s climate and clean air program, said the key question for environmental advocates is how long the administration would postpone the rule.

“It’s critical to get this standard out without delay and get onto the standards for existing sources,” Doniger said. “The deadline is coming, and if the deadline isn’t met they should expect groups like ours will take legal action to meet their responsibility.”

Frank O’Donnell, president of the advocacy group Clean Air Watch, said the EPA “set the gold standard” when it proposed requiring any new power plant emit no more CO2 than an average new U.S. gas plant.

“The question is whether this weakens it,” O’Donnell said of a possible revision. “It’s hard to see it strengthening it.”

Jeffrey Holmstead, a partner at the law firm Bracewell & Giuliani who represents several utilities, said the agency is responding to industry’s concerns that even some new natural gas plants would not be able to meet the proposed standard.

“My sense is they realize the path that started down doesn’t work,” said Holmstead, who headed EPA’s air and radiation office under George W. Bush. “This proposal is so completely different from anything they’ve done before they’ve created a problem for themselves.”

The EPA is sure to face a lawsuit once it finalizes a greenhouse gas rule for new power plants, as well as the prospect of legislation in Congress to overturn such a rule. Last year a federal appeals court overturned one of the agency’s hallmark air-quality rules, the Cross-State Air Pollution Rule, and this represents the first time EPA has ever regulated greenhouse gas emissions from a stationary source.

“They need to set a standard that will hold up in court, or otherwise it jeopardizes the entire idea of regulating greenhouse gas emissions from coal-fired power plants,” O’Donnell said.

While environmental issues don’t rank as high as jobs and the economy in the list of issues voters identify as decisive in national elections, those who care about the issue backed Obama by an overwhelming margin.

A Pew Research Center poll in April 2012 found that voters who listed the environment as top priority favored Obama by 68 to 29 percent over GOP presidential candidate Mitt Romney, the biggest margin than for any of 18 issues featured in the poll.

Capital Insight survey research analyst Scott Clement contributed to this report.