(Repeating to widen distribution)

WASHINGTON, July 14 (Reuters) - The U.S. Environmental Protection Agency said on Monday that greenhouse gas emissions endanger human health, a critical finding that has languished in bureaucratic limbo since last December.

In a 149-page document, the agency's scientists said that "warming of the climate system is unequivocal" and that potential health risks include more heat waves, floods and droughts, insect outbreaks and and wildfires, along with crop failure and decline in livestock and fisheries productivity.

"This is a long-awaited EPA analysis that has been kept under wraps by the White House," said Vickie Patton of Environmental Defense. "It's of critical importance because it looks at the extensive body of science demonstrating that global warming threatens Americans' health and well-being."

The document posted on EPA's Web site was part of the environment agency's response to an April 2007 Supreme Court ruling that for the first time found that greenhouse gases can be regulated as a pollutant under the U.S. Clean Air Act.

The idea that climate-warming greenhouse emissions threaten public health is an essential part of the Clean Air Act; policymakers must find that a substance poses this kind of threat to be designated as a pollutant, and EPA said in its documents that greenhouse gases do this.

This information had been sent to the White House last December by e-mail, but officials there refused to open it.

More than six months later, Stephen Johnson, the environment agency's chief, declined to take immediate steps to regulate planet-warming emissions, and on Friday called on Congress to act.

Instead of laying out rules, Johnson asked for public comments for a 120-day period on a nearly 1,000-page report on the effects of climate change and the ramifications of the Clean Air Act on greenhouse emissions.

Even after the initial comment period ends in November, a rule will need to be written, followed by another comment period of as much as 120 days, which makes any action during the Bush administration unlikely.

The Bush administration has opposed economy-wide moves to regulate greenhouse gas emissions. Both major presidential candidates, Republican John McCain and Democrat Barack Obama, have said they would act to stem climate change. (Editing by Eric Walsh)