WASHINGTON – 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 that affects Maine and more than a dozen other states.

On Wednesday, EPA Administrator Stephen L. Johnson blocked California and 16 other states, including Maine, that wanted to adopt California’s law slashing greenhouse gas emissions from new cars and trucks by a third.

In response, California Democrat Henry Waxman, chairman of the House Oversight and Government Reform Committee, sent a letter to 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.

In Maine, Gov. John Baldacci said the administration “has chosen to play the role of obstructionist.”

Maine Environmental Protection Commissioner David Littell said EPA was undermining efforts at the state level to combat climate change.

“The EPA is putting up roadblocks to states who have moved forward on their own to address global warming in the absence of federal leadership,” Littell said.

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.

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.

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