President Bush may be on the brink of doing something stunningly at odds with his record as one of the worst environmental stewards ever to inhabit the White House. He is considering setting aside three vast, remote corners of the Pacific Ocean for protection, an area larger than Alaska and Texas combined.

In a memo last month, Mr. Bush directed his administration to develop a plan for creating sanctuaries in the waters around the Northern Mariana Islands, including the Mariana Trench, the world’s deepest; Rose Atoll in American Samoa; and parts of a long, sprawling collection of reefs and atolls known as the Line Islands.

The waters are as isolated and pristine as any part of the globe can be these days, home to countless species of fish and plants, rare turtles and seabirds and glorious reefs. The Mariana Trench is a staggering place; it could swallow Everest. The islands are mostly coral flyspecks, but if the waters around them are protected to the fullest extent possible  to the 200-mile territorial limit  the sanctuaries would total nearly 900,000 square miles. That is bigger than all of Mexico.

Mr. Bush has done something nearly as spectacular once before. In June 2006, he created the Papahanaumokuakea Marine National Monument in the Northwest Hawaiian Islands. Over the strident objections of some commercial-fishing interests, Mr. Bush created a no-fishing sanctuary covering 140,000 square miles, an area larger than all of the country’s national parks combined.