Bush, who battled with environmentalists for years over his polices on climate change and other issues, drew further criticism at the end of his term for issuing "midnight regulations" that were viewed as ecologically unfriendly.

His changes to the Endangered Species Act were just one of a handful or such moves.

Environmental activists praised Obama's shift on Tuesday.

"Today's announcement marks the unequivocal return of science to the agencies that govern our fish, wildlife, and natural resources," said Carl Pope, executive director of environmental group Sierra Club.

"The Bush rules would have allowed agencies with little or no wildlife expertise to make decisions that could mean life or death for animals like the polar bear. When it comes to protecting wildlife, we should listen to the scientists who spend their lives studying these animals."

Representative Edward Markey of Massachusetts, who chairs a Congressional committee on energy independence and global warming, also welcomed the move.

"Today proves that, under an Obama administration, scientists are no longer an endangered species," he said in a statement. (Editing by Eric Walsh)