Congressional Democrats on Thursday announced an investigation of the Environmental Protection Agency's refusal to let California implement its tailpipe emissions law, the first step in what will likely be a fierce legal and political battle.

House Oversight and Government Reform Committee Chairman Henry Waxman, D-Calif., sent a letter to EPA Administrator Stephen L. Johnson demanding "all documents relating to the California waiver request, other than those that are available on the public record."

Waxman told Johnson to have EPA staff preserve all records. The decision against California "appears to have ignored the evidence before the agency and the requirements of the Clean Air Act," Waxman wrote. He asked for all the relevant documents by Jan. 23.

Johnson on Wednesday denied his decision was political, saying it was based on legal analysis of the Clean Air Act. His refusal blocks California and at least 16 other states that wanted to adopt California's law slashing greenhouse gas emissions from new cars and trucks by a third.

President Bush stood by the decision of his EPA administrator.

"The question is how to have an effective strategy. Is it more effective to let each state make a decision as to how to proceed in curbing greenhouse gases or is it more effective to have a national strategy," Bush said at a news conference Thursday.

Johnson said California's emissions limits weren't needed because Congress just passed energy legislation raising fuel economy standards nationwide.

"The director in assessing this law and assessing what would be more effective for the country said we now have a national plan," said Bush. "It's one of the benefits of Congress passing this legislation."

Johnson's long-awaited announcement provoked applause from the auto industry, but an outcry of protest from environmentalists, congressional Democrats and officials in California and other affected states. Gov. Arnold Schwarzenegger immediately announced plans to fight EPA's decision.

"It is completely absurd to assert that California does not have a compelling need to fight global warming by curbing greenhouse gas emissions from cars," California Attorney General Jerry Brown said. "There is absolutely no legal justification for the Bush administration to deny this request — Gov. Schwarzenegger and I are preparing to sue at the earliest possible moment."

The tailpipe standards California adopted in 2004 would have forced automakers to cut greenhouse gas emissions by 30 percent in new cars and light trucks by 2016, with the cutbacks beginning in the 2009 model year.

Under the Clean Air Act, the state needed a federal waiver to implement the rules, and other states could then adopt them too.

Johnson said a better approach was new energy legislation requiring automakers to achieve an industrywide average fuel efficiency for cars, SUVs and small trucks of 35 miles per gallon by 2020. He said California's law would have yielded a 33.8 mpg standard, but California Air Resources Board chair Mary Nichols disputed that, saying the California regulations would have resulted in a 36.8 miles per gallon average and would have taken effect sooner than the federal standards.

The auto regulations were to have been a major part of California's first-in-the-nation global warming law which aims to reduce greenhouse gases economy-wide by 25 percent — to 1990 levels — by 2020. The auto emission reductions would have accounted for about 17 percent of the state's proposed reductions.

Nichols said California expects to win on appeal and does not plan to shift its strategy on meeting greenhouse gas reduction goals.

Twelve other states — Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont and Washington — have adopted the California emissions standards, and the governors of Arizona, Colorado, Florida and Utah have said they also plan to adopt them. The rules were also under consideration in Iowa.

It was the first time EPA had completely denied California a Clean Air Act waiver request, after granting more than 50.