WASHINGTON - The head of the Environmental Protection Agency initially supported giving California and other states full or partial permission to limit tailpipe emissions — but reversed himself after hearing from the White House, a report said Monday.

The report by the Democratic staff of the House Oversight and Government Reform Committee cites sworn depositions by high-level EPA officials. It amounts to the first solid evidence of the political interference alleged by Democrats and environmentalists since Administrator Stephen Johnson denied California's waiver request in December.

Johnson's decision also blocked more than a dozen other states, including Maine, that wanted to follow California's lead and regulate greenhouse gas emissions from cars and trucks. It was applauded by the auto industry and supported by the White House, which has opposed mandatory caps on greenhouse gas emissions.

Johnson, a 27-year career veteran of the EPA, frequently has denied that his decisions are being directed by the White House. "I am the decision maker," Johnson said Monday, meeting with reporters at Platt's Energy Podium newsmaker session, before the California waiver report surfaced.

A White House spokeswoman denied interference.

"No," said Kristen Hellmer, spokeswoman for the White House Council on Environmental Quality, when asked whether the White House sought to influence Johnson on the California waiver. "He made an independent decision."

That's not what staff of the Oversight Committee, chaired by California Democratic Rep. Henry Waxman, concluded after deposing eight EPA officials and reviewing over 27,000 pages of EPA documents, some obtained under subpoena.

Perhaps the strongest evidence came from EPA Associate Deputy Administrator Jason Burnett, a political appointee.

Under oath, Burnett told committee staff that Johnson "was very interested in a full grant of the waiver" in August and September of 2007 and later thought a partial grant — allowing the waiver for two or three years — "was the best course of action."

Johnson's position changed after Johnson communicated with the White House, Burnett said.

Burnett also said there was White House input into the December letter to Gov. Arnold Schwarzenegger announcing the rationale for denying the waiver, and into the formal decision document released in February.

The committee was stymied in its attempts to discover the extent and rationale for the White House's involvement.

Burnett refused to answer questions about who Johnson talked to and when, saying EPA told him not to.

Also, EPA continues to withhold documentation of telephone calls and meetings in the White House. The committee said that the White House Counsel's office has told them EPA has 32 such documents and has described them as "indicative of deliberations at the very highest level of government."

"It appears that the White House played a significant role in the reversal of the EPA position," the report concludes. "It would appear to be inconsistent with the president's constitutional obligation to faithfully execute the laws of the United States if the president or his advisers pressured Administrator Johnson to ignore the record before the agency for political or other inappropriate reasons."

EPA spokesman Jonathan Shradar dismissed the report as "nothing new."

"Administrator Johnson was presented with and reviewed a wide range of options and made his decision based on the facts and the law," Shradar said.

"Distraction-oriented, political tactics of the committee will not keep EPA from moving forward, tackling tough issues and putting into place the most health-protective standards ever."

Shradar did not respond when asked whether it was true Johnson initially supported fully or partially granted the waiver.

The committee also found, as has been previously reported, that career EPA staff was unanimously in favor of granting the California waiver and believed that a denial would not likely stand up in court. The committee detailed previously unreported attempts by political appointees to soft-pedal EPA staff conclusions supporting the waiver in presentations to Johnson, or to avoid committing them to paper.

An internal EPA e-mail said that Bob Meyers, the principal deputy assistant administrator for the Office of Air and Radiation, was "not happy" that a staff conclusion that California met the waiver criteria was included in a briefing to Johnson last summer. Meyers' chief of staff suggested staff should "permanently delete the offending language and not have it arise again."

Because California began regulating air emissions before the federal government it has unique authority under the Clean Air Act to institute its own air rules if it gets a federal waiver. Other states can then follow California's rules or the federal ones. No waiver request had previously been fully denied.

California's law would have forced automakers to cut greenhouse gas emissions by 30 percent in new cars and light trucks by 2016, beginning with the 2009 model year. Thirteen other states already have adopted the standards — Arizona, Connecticut, Maine, Maryland, Massachusetts, New Mexico, New Jersey, New York, Oregon, Pennsylvania, Rhode Island, Vermont, and Washington.