California and 16 other states have sued to reverse the decision, and career staff had warned agency administrator Stephen Johnson that he might have to consider stepping down if he denied the waiver request.

"It is obvious to me that there is no legal or technical justification for denying this," Margo Oge, director of the EPA's Office of Transportation and Air Quality, warned in talking points prepared for a meeting with Johnson in October 2007.

"You have to find a way to get this done," Oge said in the memo obtained by the Senate Environment and Public Works Committee chaired by California Sen. Barbara Boxer, which is investigating the decision.

"If you cannot, you will face a pretty big personal decision about whether you are able to stay in the job under those circumstances," Oge said in the talking points, warning Johnson that "the eyes of the world are on you."

In a summary of another meeting with Johnson on Oct. 30, 2007, an unnamed official in the agency's climate change division said the administrator "now better appreciates that there are additional conditions in (California) that make them vulnerable to climate change."

Those include its dependence on the Pacific Northwest for much of its water, its long coast line, and a recent spate of wildfires, where "the recent news I think is helping to push (Johnson)," the staffer wrote in the e-mail, also released by the committee.

Boxer said Tuesday Johnson had gone against the advice of career staff in denying the waiver, and has introduced legislation to reverse it.

"We see more and more evidence of administrator Johnson ignoring the science and the facts, and discarding the advice of his professional staff," Boxer told a news conference, accusing the EPA and White House of "stonewalling" her attempts to obtain additional documents and data on the decision.

The EPA stood by its decision.

"The administrator made a decision based on the law and he stands by the decision," an EPA spokesman said.

California needs the waiver from the US Environmental Protection Agency to implement a state law requiring automakers to cut tailpipe carbon dioxide emissions by 25 percent on 2009 model cars.

Sixteen other states either have adopted or are considering similar rules.

In rejecting the waiver, Johnson said that a new national law, which raises automobile fuel standards by 40 percent by 2020, was a "better approach" than a "patchwork" of state rules.

Auto companies, especially struggling US-based manufacturers, fiercely opposed the attempt by California to impose new emissions regulations, which would sharply increase mileage requirements for their vehicles in that state and any others that adopted them.