The Environmental Protection Agency issued the first-ever limits on greenhouse gas emissions from new power plants Tuesday, but stopped short of imposing any restrictions on the nation’s existing coal-fired fleet.

The move sparked protests from Republicans and coal industry officials, but administration officials and most energy analysts said it would have only a modest impact because low natural gas prices are already prompting utilities to build natural gas plants instead.

The rule, which is open for public comment for 60 days, will require any new power plant to emit no more than 1,000 pounds of carbon dioxide per megawatt hour of electricity produced. The average U.S. natural gas plant, which emits 800 to 850 pounds of carbon dioxide per megawatt, meets that standard; coal plants emit an average of 1,768 pounds of carbon dioxide per megawatt.

“Today we’re taking a common-sense step to reduce pollution in our air, protect the planet for our children, and move us into a new era of American energy,” EPA Administrator Lisa P. Jackson said in a statement. She told reporters in a conference call Tuesday that the proposal “is in line with investments already being made throughout the utility industry.”

The rule, which comes on the heels of tough new requirements that the Obama administration imposed on mercury emissions and cross-state pollution from utilities within the past year, dooms any proposal to build a coal-fired plant that does not have costly carbon controls. The Washington Post first reported details of the proposal Monday.

Edison Electric Institute president Tom Kuhn, whose group represents the majority of U.S. electric utilities, said in a statement the industry is “deeply concerned” the EPA expects coal-fired plants to adopt pollution controls that will not be commercially viable for years. “By effectively forcing utilities to forgo any new coal generation in favor of natural gas, without commensurate policies to develop commercially acceptable [carbon capture and storage] technologies, EPA’s proposal threatens the viability of coal, an important domestic energy source,” he said.

Jackson said the proposal “may” affect 15 power plants in the permitting pipeline, but even that estimate may be high: The Energy Information Administration estimates only one 900-megawatt coal-fired power plant will probably be built between now and 2030.

“The message here is it’s not costing jobs; the market has already shifted,” said Ned Helme, president of the Center for Clean Air Policy, noting that gas plants employ the same number of workers but emit about half the carbon of coal plants. “It’s simply a shift from a dirtier fuel to a cleaner fuel.”

Rep. Edward J. Markey (D-Mass.) said in a statement that the new regulation provides a new incentive for the United States to think twice before approving eight natural gas export terminal proposals, which according to the Energy Department could export 20 percent of the nation’s total gas production.

“This carbon standard is yet another indication that we need to keep America’s natural gas here at home to provide affordable electricity and capitalize on our competitive advantage to rebuild our manufacturing, chemical and fertilizer industries,” Markey said.

Republicans in both chambers of Congress said they would seek to overturn the rule through legislative means.

“We were successful in stopping their job-killing agenda through legislation when we defeated cap-and-trade. Now our fight is to stop them from forcing it on the American people through regulations,” said Sen. James M. Inhofe (Okla.), the top Republican on the Senate Environment and Public Works Committee.

Some advocacy groups, however, called the proposal too weak because it failed to cover existing power plants, which emit more than 2 billion tons of greenhouse gas emissions a year, or roughly a third of the nation’s total.

Michael Livermore, executive director of New York University’s Institute for Policy Integrity, called the failure to cover existing plants “a big problem,” noting that the move might encourage utilities to keep conventional coal plants operating longer.

“When you want to reduce pollution, you need to go where the pollution is, and that’s existing sources,” he said, adding that when the government grandfathers existing plants and raises the standards for building new ones, “you increase the incentives to keep existing facilities around.”

Jason S. Grumet, president of the Bipartisan Policy Center, said the issues with the rule highlighted the fact that there is no overarching national climate policy.

“The Congress and courts are forcing EPA to use a 1990 public health statute to address a global challenge that was largely unappreciated at the time. In the absence of additional congressional action, no faction or party will be satisfied with these regulatory outcomes,” he said.

The rule provides an exception for coal plants that are already permitted and beginning construction within a year. It also provides some flexibility by judging utilities’ compliance with the rule over 30 years, allowing super-efficient coal plants an exemption for the first decade of operation before requiring them to reduce their carbon emissions by more than 50 percent.