The Obama administration is warning Congress that if it doesn't move to regulate greenhouse gases, the Environmental Protection Agency will take a "command-and-control" role over the process in a way that could hurt business. 

The warning, from a top White House economic official who spoke Tuesday on condition of anonymity, came on the eve of EPA Administrator Lisa Jackson's address to the international conference on climate change in Copenhagen, Denmark.

Jackson, however, tried to strike a tone of cooperation in her address Wednesday, explaining that the EPA's new powers to regulate greenhouse gases will be used to complement legislation pending in Congress, not replace it.

"This is not an 'either-or' moment. It's a 'both-and' moment," she said.

But while administration officials have long said they prefer Congress take action on climate change, the economic official who spoke with reporters Tuesday night made clear that the EPA will not wait and is prepared to act on its own. 

And it won't be pretty. 

"If you don't pass this legislation, then ... the EPA is going to have to regulate in this area," the official said. "And it is not going to be able to regulate on a market-based way, so it's going to have to regulate in a command-and-control way, which will probably generate even more uncertainty." 

Climate change legislation that passed the House is stuck in the Senate, but the EPA finding Monday was seen as a boost to the U.S. delegation in Denmark trying to convince other countries that Washington is capable of taking action to follow through with any global commitments. 

The economic official explained that congressional action could be better for the economy, since it would provide "compensation" for higher energy prices, especially for small businesses dealing with those higher energy costs. Otherwise, the official warned that the kind of "uncertainty" generated by unilateral EPA action would be a huge "deterrent to investment," in an economy already desperate for jobs. 

"So, passing the right kind of legislation with the right kind of compensations seems to us to be the best way to reduce uncertainty and actually to encourage investment," the official said. 

Republicans fear that the EPA will ultimately end up stepping in to regulate emissions -- though many oppose the congressional legislation as well. They had urged Jackson to withdraw the finding in light of leaked e-mails from a British research center that appeared to show scientists discussing the manipulation of climate data. 

Rep. James Sensenbrenner, R-Wis., ranking Republican on the House Select Committee for Energy Independence and Global Warming, said Tuesday he is going to attend the Copenhagen conference to inform world leaders that despite any promises made by President Obama, no new laws will be passed in the United States until the "scientific fascism" ends. 

"I call it 'scientific fascism,'" Sensenbrenner said during a press conference with fellow climate change skeptics. Sensenbrenner said, "The U.N. should throw a red flag" on scientists who support global warming to the exclusion of dissent. 

Administration officials, though, said the e-mails do not change the debate. 

Former Vice President Al Gore, a leader in the movement on man-caused climate change, told CNN on Wednesday that the e-mails in questions were 10 years old and taken "out of context." 

Fox News' Major Garrett and The Associated Press contributed to this report.