A U.S. Environmental Protection Agency proposal that could lead to regulating the gases blamed for global warming will prove costly for factories, small businesses and other institutions, according to a White House document.

The nine-page memo is a compilation of opinions made by a dozen federal agencies and departments before the EPA determined in April that greenhouse gases pose dangers to public health and welfare.

That finding set in motion the regulation of six heat-trapping gases from cars and trucks, factories and other sources under the Clean Air Act for the first time.

The document, labeled "Deliberative-Attorney Client Privilege," says that if the EPA proceeds with the regulation of heat-trapping gases, including carbon dioxide, factories, small businesses and institutions would be subject to costly regulation.

"Making the decision to regulate carbon dioxide ... for the first time is likely to have serious economic consequences for regulated entities throughout the U.S. economy, including small businesses and small communities," the document reads.

A White House aide and Office of Management and Budget spokesman said the cost critique came from a single federal agency, and the document did not reflect the administration's view. They declined to identify which agency challenged the EPA proposal.

When the Bush administration unveiled its proposal to use the Clean Air Act to regulate greenhouse gases, it released full comments from each individual agency -- many of which were critical. The Bush White House ultimately decided against using the Clean Air Act, saying it was an imperfect tool that would burden the economy.

Unlike former President George W. Bush, President Barack Obama has offered an alternative -- a new law that would limit and put a price on greenhouse gas pollution.

"The president has called on Congress to pass comprehensive energy legislation that includes a market based cap on carbon emissions that would transition the nation to a clean energy economy and create millions of green jobs," said Ben LaBolt, a White House spokesman.

New legislation, currently being considered by the House, would mostly pre-empt the agency from regulating greenhouse gases under existing law. The bill may also help mitigate some of the costs to businesses by distributing some of the permits for free.

Still, Republicans and business groups immediately used the document to bolster their arguments that controlling greenhouse gases would harm the economy.

They also highlighted parts of the document that fault how the EPA arrived at its conclusion that greenhouse gases endanger human health and welfare, since the gases by themselves do not pose any harm.

The memo says the EPA could have been "more balanced" in its analysis by also highlighting regions of the country that would benefit from global warming, such as the state of Alaska, which would have warmer winters. It also says the EPA appeared to stretch the precautionary principle to support regulation despite the "unprecedented uncertainty" in linking emissions of greenhouse gases and the warming that will result to health effects.

"It really appears to me that the decision was based more on political calculation than on scientific ones," said Sen. John Barrasso, R-Wyo., who called the document "a smoking gun" during a hearing Tuesday on the Obama administration's proposed budget for EPA.

"The counsel in this administration repeatedly questions the lack of scientific support that you have for this proposed finding," he said.

EPA administrator Lisa Jackson responded by saying the EPA's finding in April was required by law, stemming from a 2007 Supreme Court decision that said the agency should classify greenhouse gases as pollutants. Jackson also said the agency's determination was preliminary and would not necessarily result in regulation.

"I have said over and over, as has the president, that we do understand that there are costs to the economy of addressing global warming emissions, and that the best way to address them is through a gradual move to a market-based program like cap and trade," Jackson said.