Government scientists, armed with copies of heavily edited reports, charged Monday that the Bush administration and its political appointees had soft-pedaled their findings on climate change.

The accusations led Democrats and Republicans at the congressional hearing to accuse each other of censorship, smear tactics and McCarthyism.

To underscore their charges of the administration's oil-friendly stance, Democrats grilled an oil lobbyist who was hired by the White House to review government climate change documents and who made hundreds of edits that the lawmakers said minimized the impact of global warming.

"You were a spin doctor," Rep. John A. Yarmuth (D-Ky) told the lobbyist.

Republicans targeted a NASA director who testified about administration pressure, accusing him of political bias, of politicizing his work and of ignoring uncertainties in climate change science.

And they disputed his contention that taxpayer-funded scientists are entitled to free speech. "Free speech is not a simple thing and is subject to and directed by policy," said Rep. Chris Cannon (R-Utah).

The House Committee on Oversight and Government Reform hearing was marked by an open confrontation between Chairman Henry A. Waxman (D-Los Angeles) and the ranking Republican, Rep. Darrell Issa (R-Vista) — a rare display of direct debate in otherwise carefully choreographed hearings.

The hearing was the latest effort to challenge what the Democratic congressional majority sees as the Bush administration's unchecked use of power. In the past few weeks, Democrats have held inquiries or announced plans to examine the unmonitored use of national security letters that allow the government to spy on Americans, the dismissal of U.S. attorneys and the identifying of former covert CIA operative Valerie Plame, among other issues.

Waxman has been particularly aggressive, pursuing inquiries about intelligence in the lead-up to the Iraq war and the politics of global warming.

To support their charges Monday, the Democrats produced hundreds of pages of legal depositions, exhibits and e-mail exchanges between administration officials. The paper trail illustrated how officials with no scientific training shaped the administration's climate change message and edited global warming reports, inserting doubt in the place of definitive statements and diminishing the role people play in the planet's rising temperatures.

Waxman's committee received more than eight boxes of papers from the White House Council on Environmental Quality that he said provided disturbing indications of political interference.

"There may have been a concerted effort directed by the White House to mislead the public about the dangers of global climate change," said Waxman, who also cited the administration practice of "controlling what federal scientists could say to the public and the media about their work."

"It would be a serious abuse if senior White House officials deliberately tried to defuse calls for action by ensuring that the public heard a distorted message about the risks of climate change," Waxman said.

One example showed how a report originally said the U.S. National Research Council had concluded that "greenhouse gases are accumulating in the atmosphere as a result of human activities, causing surface air temperatures to rise and subsurface ocean temperatures to rise."