By Valerie Volcovici

WASHINGTON (Reuters) - U.S. federal agencies should disclose whether their actions and decisions will have an impact on climate change, the White House announced on Tuesday.

The White House Council on Environmental Quality (CEQ) finalized an update after nearly six years of consultations of the National Environmental Policy Act (NEPA), a Nixon-era statute that called on officials to weigh the environmental effects of projects such as highways, dams or oil drilling.

The update takes NEPA a step further by requiring agencies such as the Interior Department to the Army Corps of Engineers to quantify greenhouse gas emissions in NEPA project reviews and to describe the potential climate change impacts.

"This increased predictability and certainty will allow decision makers and the public to more fully understand the potential climate impacts of all proposed federal actions," the CEQ said in a statement.

This would prompt agencies to consider alternatives or propose measures to mitigate the climate impacts of a project, it said.

Since the CEQ first proposed to modify NEPA in 2010 to include weighing climate change impacts, Republican lawmakers have discouraged the move saying it would be a way for the Obama administration to regulate carbon emissions without congressional approval.

President Barack Obama has used executive authority to use the federal Clean Air Act to regulate greenhouse gas emissions from power plants, oil and gas infrastructure and energy development on public lands.

Rhea Suh, president of the Natural Resources Defense Council, said the CEQ's announcement is "a game-changer" that would ensure that federal agencies do not "approve mines that will destroy the climate, or bridges that will get washed away."

Conservation group The Wilderness Society said the CEQ guidance will ensure that decisions about whether to allow energy exploration or development on federal land do not contribute to climate change.

"Federal land management agencies should implement this guidance without delay, and use cutting-edge science to make climate-smart decisions," the group said.

The Republican chair of the House committee on natural resources, which deals with federal land policies, said the new CEQ guidance would trigger lawsuits and effectively block every major energy or infrastructure project.

"Finding the practical and legal basis for this guidance deserves a Gold Medal for mental gymnastics," said Utah Congressman Rob Bishop. "When any emissions equals bad and bad equals denied, you can kiss energy independence goodbye.”

(Reporting by Valerie Volcovici; Editing by Diane Craft and Sandra Maler)