By Jeff Mason
Bush, who often draws ire from activists for his record on environmental issues, will declare three areas in the central Pacific "marine national monuments," spokeswoman Dana Perino said.
"The president's actions will prevent the destruction and extraction of natural resources from these beautiful and biologically diverse areas without conflicting with our military's activities and freedom of navigation, which are vital to our national security," she told a briefing.
She said the new protected areas will comprise the largest area of ocean set aside as marine protected areas in the world, at 195,280 square miles (505,500 sq km).
The areas are home to huge underwater mud volcanoes, coral reefs, and rare species of whales among other things.
The White House said in August it would consider a group of islands and atolls in the remote central Pacific, including the Rose Atoll near American Samoa, and some of the waters around the Northern Mariana Islands in the western Pacific for protection.
James Connaughton, chairman of the White House Council on Environmental Quality, told reporters on Monday the three areas decided upon included the Mariana National Monument, Pacific Remote Islands National Monument, and the Rose Atoll.
Bush established a national monument in the northwestern Hawaiian Islands in 2006, creating the largest marine protected area in the world at the time.
The Pew Environment Group praised the latest decision.
"This historic action by President Bush protects some of the world's most unique and biologically significant ocean habitat," Joshua Reichert, the group's managing director, said in a statement.
"Together with the Hawaii marine monument established two years ago, this marks the end of an era in which humans have increasingly understood the need to conserve vanishing wild places on land but failed to comprehend the similar plight of our oceans. It comes none too soon."
Earlier this year Bush lifted a White House ban on offshore drilling closer to home as gasoline prices were soaring. Environmentalists said that largely symbolic move would hurt wildlife while doing little to bring down fuel prices.
(Editing by Sandra Maler)