The White House announced over the weekend that Philip Cooney, chief of staff of its Council on Environmental Quality, had resigned, calling it a long-planned departure. He had been head of the climate program at the American Petroleum Institute, the trade group for large oil companies.

Cooney will join ExxonMobil in the fall, company spokesman Russ Roberts told The Associated Press in a telephone interview from its Dallas headquarters. He declined to described Cooney's job.

Cooney could not be reached through the White House for comment.

White House spokeswoman Dana Perino said Cooney's departure was "completely unrelated" to the disclosure two days earlier that he had made changes in several government climate change reports that were issued in 2002 and 2003.

"Mr. Cooney has long been considering his options following four years of service to the administration," Perino said. "He'd accumulated many weeks of leave and decided to resign and take the summer off to spend time with his family."

The White House made no mention of Cooney's plans to join ExxonMobil, the world's largest oil company. Its executives have been among the most skeptical in the oil industry about the prospects of climate change because of a growing concentration of heat-trapping gases in the atmosphere. The leading greenhouse gas is carbon dioxide from burning fossil fuels.

Like the Bush administration, ExxonMobil Chairman Lee Raymond has argued strongly against the Kyoto climate accord and has raised questions about the certainty of climate science as it relates to possible global warming. Greenpeace and other environmental groups have singled out Raymond and ExxonMobil for protests because of its position on climate change.

Last week, the Government Accountability Project, a nonprofit group that helps whistleblowers, made available documents showing that Cooney was closely involved in final editing of two administration climate reports. He made changes that critics said consistently played down the certainty of the science surrounding climate change.

After Cooney's involvement in editing the climate reports was first reported by The New York Times, the White House defended the changes, saying they were part of the normal, wide-ranging review process and did not violate an administration pledge to rely on sound science.

A whistleblower, Rick Piltz, who resigned in March from the government office that coordinates federal climate change programs, made the documents — showing handwritten edits by Cooney — available to the Project on Government Accountability and, in turn, to news media.