WASHINGTON — A rule proposed by the Enivironmental Protection Agency would cut carbon pollution from power plants 30 percent from 2005 levels by 2030 – the equivalent, according to the agency, of taking two-thirds of all cars and trucks in America off the road. Here are some things to know about the rule:

• The E.P.A. expects that under the regulation, 30 percent of electricity in the United States will still come from coal by 2030, down from about 40 percent today.

• The E.P.A. 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 percent by 2020 and press other major polluting countries, particularly China and India, to follow suit.