(Adds confirmation of proposed targets, details of expected plan)
WASHINGTON, June 1 (Reuters) - The U.S. Environmental Protection Agency plans on Monday to propose a 30 percent cut in carbon dioxide emissions from the country's existing power plants by 2030, people briefed on the proposal told Reuters.
Word of some of the proposal's components came before Monday's unveiling by EPA Administrator Gina McCarthy. They mark the most sweeping and significant environmental regulations introduced by the Obama administration.
Although states will be given different targets to meet depending on the carbon intensity of their current power plants, the power sector would need to reduce carbon dioxide emissions by 25 percent on average by 2020 and hit the 30 percent target 10 years later, the sources said.
The proposed reductions would be based on 2005 emissions, the baseline the White House used to set a global goal to slash greenhouse gas emissions 17 percent by 2020.
The target was first reported by the Wall Street Journal on Sunday. The White House and the EPA declined to confirm or comment on the rules before they are released.
Several lawmakers were briefed on the proposal on Sunday, including Democrats Sheldon Whitehouse of Rhode Island and Edward Markey of Massachusetts, two of the Senate's biggest supporters of measures to address global warming.
One industry source said the agency had wrestled with which year to set as the baseline for the pollution cuts.
Energy-related carbon emissions fell after 2008 because of a shift toward cleaner-burning natural gas and away from coal-fired plants, and the severe economic downturn.
Emissions in 2013 were already slightly more than 10 percent below 2005 levels, according to the Energy Information Administration, meaning the United States is already well down the road to meeting to new targets.
CASTING IT AS PUBLIC HEALTH ISSUE
The EPA will likely give states a range of options to meet the target, and may establish different timelines to allow states that are heavy users of coal - Kentucky and West Virginia, for example - to catch up, sources have said.
As well as improving the energy efficiency of their power plants and using more zero-carbon electricity sources such as nuclear and renewables, states are expected to be allowed by the EPA to use emissions trading systems to comply.
States like California and nine Northeastern states have been using carbon markets to cut emissions for several years.
Facing opposition from some state governments, the coal industry and pro-business groups like the U.S. Chamber of Commerce, the administration has cast the regulations as a public health issue.
The United States had to do more to help children suffering from asthma and other related ailments, President Barack Obama said on Saturday in his weekly radio address.
Obama will participate in a conference call on Monday with health groups hosted by the American Lung Association to discuss the regulations, before leaving Washington for a trip to Europe. (Reporting by Valerie Volcovici, Jeff Mason,; Additional reporting by Mark Felsenthal Editing by Ros Krasny, Jim Loney and Peter Cooney)