WASHINGTON — On Monday, the Obama administration announced one of the strongest actions ever taken by the U.S. government to fight climate change, a proposed Environmental Protection Agency regulation to cut carbon pollution from the nation’s power plants by 30% from 2005 levels by 2030.

The regulation takes aim at the largest source of carbon pollution in the United States, the nation’s more than 600 coal-fired power plants. If it withstandsan expected onslaught of legal and legislative attacks, experts say that it could close hundreds of the plants and also lead, over the course of decades, to systemic changes in the American electricity industry, including transformations in how power is generated and used.

Below, the New York Times summarizes key elements from the EPA announcement:

• The EPA expects that under the regulation, 30% of electricity in the United States will still come from coal by 2030, down from about 40% today.
• The EPA estimates that the rule will cost the economy $7.3 billion to $8.8 billion annually, but will lead to benefits of $55 billion to $93 billion, primarily by preventing premature deaths and mitigating respiratory diseases.
• Critics complain that the rule will drive up electricity costs, but the agency forecasts that the rule will increase energy efficiency across the power sector, leading to lower electricity bills when the program is fully implemented in 2030.
• The rule will not, on its own, lower greenhouse gas pollution enough to prevent catastrophic effects of climate change. But, in combination with other regulations, it would allow the United States to meet its commitment to the United Nations to cut carbon pollution 17% by 2020 and press other major polluting countries, particularly China and India, to follow suit.
• The draft proposal is just the beginning of the process to cut emissions. The agency will now take public comment and spend the next year completing the proposal before releasing the final rule in June 2015. States will then be given another year to submit compliance plans or apply for an extension.
• The rule is not an executive order. Under the Clean Air Act, the EPA is required to regulate any substance defined as a pollutant, which the law defined as substances that endanger human life and health. A 2007 Supreme Court decision led to an EPA determination that carbon dioxide is a pollutant, thus requiring that the agency regulate it or be in violation of the law.