This month, the Environmental Protection Agency will propose standards that will establish stricter pollution limits for gas-fired power plants than coal-fired power plants, according to individuals who were briefed on the matter but asked not to be identified because the rule was not public yet.

The revised rule, which would impose greenhouse gas limits on power plants for the first time, will still require utilities to install costly carbon controls on coal plants.

The agency initially proposed that any new power plant emit no more than 1,000 pounds of carbon dioxide per megawatt hour of electricity produced but decided to overhaul that rule this spring out of concern that it would face a stiff legal challenge.

The average U.S. natural gas plant emits 800 to 850 pounds of carbon dioxide per megawatt, and coal plants emit an average of 1,768 pounds. According to those familiar with the new EPA proposal, the agency will keep the carbon limit for large natural gas plants at 1,000 pounds but relax it slightly for smaller gas plants. The standard for coal plants will be as high as 1,300 or 1,400 pounds per megawatt hour, the individuals said Wednesday, but that still means the utilities will have to capture some of the carbon dioxide they emit.

During his climate speech in June, President Obama described establishing a carbon rule for new plants as part of his overall plan to address global warming.

EPA spokeswoman Alisha Johnson declined to provide details on the rule, which is set to be released Sept. 20. She wrote in an e-mail that the agency “is working to finalize its re-proposal of a pollution standard for new power plants in light of the important comments received by the agency and in a way that considers the viewpoints of all stakeholders.”

“President Obama is committed to taking action for our kids by cutting pollution and addressing climate change in a way that protects public health and helps develop a stronger economy through science, research and innovation,” she added.

Jeffrey R. Holmstead, a partner at the Bracewell & Giuliani law firm who represents several companies that operate coal-fired plants, said the Obama administration “has told several industry folks that the new proposal will have a slightly higher standard for coal.” Holmstead said the carbon capture and storage requirement will make it impossible to build new coal plants.

“As a practical matter, this means that the new proposal will still stop any new coal-fired power plants for the foreseeable future,” said Holmstead, who headed EPA’s air and radiation office under President George W. Bush. “Given the cost of carbon capture and all the other problems associated with it, any rule that requires [it] will effectively prohibit the construction of new coal-fired plants.”