Cars, power plants and factories in the United States could all soon face much tougher pollution limits after a government declaration Friday set the stage for the first federal regulation of gases blamed for global warming.

The U.S. Environmental Protection Agency took a big step in that direction, concluding that carbon dioxide and five other greenhouse gases are a major hazard to Americans' health.

That was a reversal from former president George W. Bush's administration, which resisted such a conclusion and said it would be costly for companies to meet new emission limits and therefore could harm the national economy.

"In both magnitude and probability, climate change is an enormous problem [and] the greenhouse gases that are responsible for it endangered public health and welfare," said the EPA, concluding the dangers warrant action under federal air pollution laws.

It was the first time the federal government had said it was ready to use the Clean Air Act to require power plants, cars and trucks to curtail their release of climate-changing pollution, especially carbon dioxide from the burning of fossil fuels.

The agency said the science pointing to man-made pollution as a cause of global warming is "compelling and overwhelming." It also said tailpipe emissions from motor vehicles contribute.

EPA administrator Lisa Jackson cautioned that regulations are not imminent and made clear that the Obama administration would prefer that Congress address the climate issue through a broader "cap-and-trade" program that would limit heat-trapping pollution.