The Arctic National Wildlife Refuge covers only a small part of Alaska. Smaller still is the coastal plain of the refuge, a narrow, 1.5 million-acre strip flanking the Beaufort Sea. The plain is an ecological and biological wonder, the hunting grounds for Alaskan natives and home to caribou, polar bears, all manner of marine life and countless bird species. It may also contain one of the biggest unexploited oil fields in America.

For all these reasons, the plain has been the subject of a bitter tug of war between politicians and oil companies that covet its commercial resources, on one side, and conservationists who think that opening it would be a calamity — “the equivalent,” the former secretary of the interior Bruce Babbitt once said, “of offering Yellowstone National Park for geothermal drilling, or calling for bids to construct hydropower dams in the Grand Canyon.”

President Obama has now come down emphatically on the side of conservation. At the recommendation of Sally Jewell, his secretary of the interior, and John Podesta, his senior counselor, Mr. Obama proposed on Sunday to set aside more than 12 million acres of the refuge as permanent wilderness, including the 1.5 million acres of the coastal plain. Wilderness designation is the highest level of protection the government can confer on public land. It would bar commercial development of any kind, including, crucially, oil-and-gas exploration.