The Bush administration has decided to propose listing the polar bear as threatened under the Endangered Species Act, putting the U.S. government on record as saying that global warming could drive one of the world's most recognizable animals out of existence.

The administration's proposal -- which was described by an Interior Department official who spoke on the condition of anonymity -- stems from the fact that rising temperatures in the Arctic are shrinking the sea ice that polar bears need for hunting. The official insisted on anonymity because the department will submit the proposal today for publication in the Federal Register, after which it will be subject to public comment for 90 days.

Identifying polar bears as threatened with extinction could have an enormous political and practical impact. As the world's largest bear and as an object of children's affection as well as Christmastime Coca-Cola commercials, the polar bear occupies an important place in the American psyche. Because scientists have concluded that carbon dioxide from power-plant and vehicle emissions is helping drive climate change worldwide, putting polar bears on the endangered species list raises the legal question of whether the government would be required to compel U.S. industries to curb their carbon dioxide output.

"We've reviewed all the available data that leads us to believe the sea ice the polar bear depends on has been receding," said the Interior official, who added that U.S. Fish and Wildlife Service officials have concluded that polar bears could be endangered within 45 years. "Obviously, the sea ice is melting because the temperatures are warmer."

Northern latitudes are warming twice as rapidly as the rest of the globe, according to a 2004 scientific assessment, and by the end of the century annual ocean temperatures in the Arctic may rise an additional 13 degrees Fahrenheit. As a result, researchers predict that summer sea ice, which polar bears use as a platform to hunt for ringed seals, will decline 50 to 100 percent. Just this month, researchers at the National Center for Atmospheric Research outlined a worst-case scenario in which summer sea ice could disappear by 2040.

By submitting the proposal today, the Interior Department is meeting a deadline under a legal settlement with three environmental advocacy groups -- the Center for Biological Diversity, the Natural Resources Defense Council and Greenpeace -- that argue the government has not responded quickly enough to the polar bear's plight. The department has been examining the status of polar bears for more than two years.

NRDC senior attorney Andrew Wetzler, one of the lawyers who filed suit against the administration, welcomed the proposal for listing.

"It's such a loud recognition that global warming is real," Wetzler said. "It is rapidly threatening the polar bear and, in fact, an entire ecosystem with utter destruction."

There are 20,000 to 25,000 polar bears worldwide, 4,700 of which live in Alaska and spend part of the year in Canada and Russia. The other countries with polar bears in their Arctic regions are Denmark (Greenland) and Norway.

Although scientists have yet to fully assess many of the 19 separate polar bear populations, initial studies suggest that climate change has already exacted a toll on the animals.

The ice in Canada's western Hudson Bay breaks up 2 1/2 weeks earlier than it did 30 years ago, giving polar bears there less time to hunt and build up fat reserves that sustain them for eight months before hunting resumes. As local polar bears have become thinner, female polar bears' reproductive rates and cubs' survival rates have fallen, spurring a 21 percent population drop from 1997 to 2004.

Scientists have not charted the same rapid decline within the U.S. polar bear populations, but federal scientists have observed a number of troubling signs. The bears have resorted to open-water swimming and even cannibalism in an effort to stay alive.

Polar bears normally swim from one patch of sea ice to another to hunt for food, but they are not accustomed to going long distances. In September 2004, government scientists observed 55 polar bears swimming offshore in the Alaskan Beaufort Sea, an unprecedented spike, and four of those bears died. In a separate study that year, federal scientists identified three instances near the Beaufort Sea in which polar bears ate one another.

The Interior official said government officials studying Alaskan polar bears in the southern Beaufort Sea area have observed thinner adult bears and a lower rate of survival among cubs. Although the population has yet to dip, "unless the polar cub survival rate goes up, it would have to happen," the official said.

Still, the official added that the decision to propose polar bears as threatened with extinction "wasn't easy for us" because "there is still some significant uncertainty" about what could happen to bear populations in the future.

"This proposal is sort of like a scientific hypothesis. You put this out there and say to the world, 'Tell us, is this right or is this wrong?' " the official said, adding that Interior will hold several public hearings about its proposal. "We're projecting what we think will happen in the future, not just what's happening at this moment."

The department could take up to a year to complete its proposal, and it could abandon the listing if it unearths new scientific projections about the bears' fate. But that appears unlikely, as recent models have consistently pointed to a faster deterioration of Arctic sea ice.

Although federal officials cited rising sea temperatures once before in a threatened-species proposal -- in May, when they called them a "major stressor" on Caribbean elkhorn and staghorn corals -- today's proposal will mark the first time the administration has identified climate change as the driving force behind the potential demise of a species.

Robert Correll, the scientist who chaired the international Arctic Climate Impact Assessment in 2004, said in an interview that the proposal to place polar bears on the endangered species list is "highly justified."

Correll, now directs the global change program at the H. John Heinz III Center for Science, Economics and the Environment, added that he is participating in an administration-funded study at the Center for Strategic and International Studies on how climate change could affect national security and foreign policy.

That, along with the proposal on polar bears, he said, "plays into a reality that, in my opinion, they're going to be rethinking their position" on global warming.

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