WASHINGTON — The Environmental Protection Agency took a historic step on Tuesday in the fight against climate change, proposing the first limits of greenhouse gas emissions from new power plants.

WASHINGTON — The Environmental Protection Agency took a historic step on Tuesday in the fight against climate change, proposing the first limits of greenhouse gas emissions from new power plants.

The new rule likely would make new coal-fired power plants too expensive after this year. It wouldn't apply to some 15 power plants that are expected to break ground in the next 12 months. After that, however, coal-fired plants would have to capture and store some of their carbon dioxide emissions, a practice that's so costly it isn't in commercial use anywhere.

Natural gas plants belch only about half the emissions of coal plants and would not need any additional equipment to meet the new standard. The nation's utilities have been moving toward natural gas to fuel new plants anyway, since the use of hydraulic fracturing has greatly expanded the nation's gas supply and prices are down.

This is the first time that the U.S. has ever proposed any limits on greenhouse gases from industrial sources. Republicans in Congress and their business allies vowed to fight the EPA rule as hostile to abundant coal and too costly. Environmentalists and health groups cheered it.

Scientists have amassed a huge body of evidence and documented research showing that these gases in the atmosphere, mostly from burning fossil fuels, are driving ocean acidification and global warming.

"We know the potential impacts of climate change touch everything from tourism to agriculture and will have an extraordinary environmental and economic footprint if allowed to proceed unchecked," said EPA Administrator Lisa Jackson. "And when we see the extraordinary potential for cleaner, cheaper energy for the American people and the chance to lead a global marketplace for clean-energy technology, it is clear that we must take action."

The standard will have limited impact, however, because it won't apply to existing power plants, the biggest industrial source of greenhouse gases. Also exempt are new plants that already have permits and will break ground in the next 12 months.

Jackson said the EPA has no plans to address emissions from existing plants. U.S. power plants produced 2.3 billion metric tons of carbon dioxide in 2010, about one-third of the nation's total emissions.

She addressed economic criticism by saying that the new standard takes advantage of abundant natural gas and imposes no costs on current plants. She also said that coal would remain a major part of the U.S. energy mix, citing Energy Department forecasts.

Coal now generates 45 percent of electricity. The department expects it will still provide 29 percent in 2035.