A White House official edited government reports in ways that played down links between global warming and emissions, the New York Times reported.
The documents outlined US climate change policy
Philip Cooney removed or adjusted descriptions of climate research that had already been approved by government scientists, the newspaper said.
The White House denied Mr Cooney, a former oil industry advocate, watered down the reports.
It said the changes were part of a normal inter-agency review process.
The reports were "based on the best available science", spokesman Scott McClellan said.
Mr Cooney is chief of staff for the White House Council on Environmental Quality, which helps devise and promote the administration's policies on environmental issues.
The administration of President George W Bush has consistently questioned the need for quick action on climate change, and the US has refused to ratify the Kyoto Protocol aimed at cutting down greenhouse gas emissions.
Before working at the White House, Mr Cooney was a lobbyist at the American Petroleum Institute, the largest oil industry trade group.
He is a lawyer by training, with no scientific background.
The New York Times said he made dozens of changes to reports issued in 2002 and 2003, and many appeared in final versions of major administration climate reports.
They included the insertion of the phrase "significant and fundamental" before the word "uncertainties", and tended to produce an air of doubt about findings most climate experts say are robust, the paper reported.
In another instance, the paper said Mr Cooney added the word "extremely" to the sentence, "The attribution of the causes of biological and ecological changes to climate change or variability is extremely difficult."
The newspaper obtained the documents from the Government Accountability Project, a non-profit group that provides legal assistance to whistle-blowers.
The project is representing Rick Piltz, who resigned in March from the office that co-ordinates government climate research and which issued the documents that Mr Cooney edited.