The Obama administration today unveiled a sweeping new plan that aims to cut carbon dioxide emissions from the nation’s 600 coal-fired power plants by roughly a third. Gina McCarthy, administrator of the U.S. Environmental Protection Agency, said the new rules would give states maximum flexibility to achieve the goal of reducing power plant emissions 30 percent below 2005 levels by 2030. Hundreds of coal-fired power plants are expected to close under the EPA plan. But rather than immediately shutting down plants, states would be allowed to reduce emissions by making changes across their electricity systems — by installing new wind and solar generation or energy-efficiency technology, continuing to expand the use of natural gas, and by starting or joining state and regional “cap and trade” programs. “There is no one-size-fits-all solution … so each state’s path can be different,” said McCarthy. The proposed regulations could be held up by legal challenges. Obama administration officials said the rules would lift the U.S. into a clear global leadership position on combating global warming.