In announcing the government's decision one day ahead of a court-ordered deadline, Interior Secretary Dirk Kempthorne acknowledged that human-caused greenhouse gas emissions contribute to the global warming that is damaging the polar bears' habitat.

However, he stressed that the threatened status could not properly be used to regulate greenhouse emissions.

"While the legal standards under the Endangered Species Act compel me to list the polar bear as threatened, I want to make clear that this listing will not stop global climate change or prevent any sea ice from melting," he said at a briefing.

"Any real solution requires action by all major economies for it to be effective," Kempthorne said. He also noted he was taking administrative and regulatory action to ensure this decision is not "abused to make global warming policies."

The proper forum for combating climate change is among the world's major economies, Kempthorne said. The Bush administration has convened the world's worst greenhouse polluting nations in a series of international meetings.

Polar bears live only in the Arctic and depend on sea ice as a platform for hunting seals. The US Geological Survey said two-thirds of the world's polar bears -- some 16,000 -- could be gone by 2050 if predictions about melting sea ice hold true.

This is the first time climate change has been a factor in proposing a threatened status for any US species, and was spurred on by environmentalists who claimed a limited victory in Kempthorne's announcement.

"MAJOR STEP FORWARD" WITH "LOOPHOLES"

"Protecting the polar bear under the Endangered Species Act is a major step forward, but the Bush administration has proposed using loopholes in the law to allow the greatest threat to the polar bear -- global warming pollution -- to continue unabated," Andrew Wetzler of the Natural Resources Defence Council said in a statement.

John Kostyack of the National Wildlife Federation, while gratified at the listing, saw little practical effect given the limits of Kempthorne's regulations.

"By denying a direct link between the sources of global warming pollution and the loss of the polar bears' sea ice habitat, and by denying that the polar bear will be protected from oil and gas development, they're willing to sit by and let the polar bear go extinct," Kostyack said by telephone.

The Endangered Species Act requires that decisions to protect wildlife be based solely on science, not on economic factors.

Kempthorne said his administrative rule aims at defining the scope of the decision, and at "limiting the unintended harm to the society and the economy of the United States."

Bill Kovacs of the US Chamber of Commerce praised the decision and its accompanying regulations, calling is a "common sense balancing" between environmental and business concerns.

Without the limiting regulations, Kovacs said, all carbon-emitters in the contiguous United States would have to go through a consultation process, which he said would have literally shut down federal activity overnight.

Wednesday's decision was one day ahead of a court-ordered deadline. The US government was initially supposed to decide in January but postponed its decision, citing the volume of scientific data to be considered.

In February, the Interior Department sold oil and gas rights across some 29.7 million acres (12.02 million hectares) of the Chukchi Sea off the Alaskan coast -- including prime polar bear habitat -- for a record $2.66 billion.

Canada, home to two-thirds of the world's polar bears, will not for now follow the US lead in listing the animals as threatened, Environment Minister John Baird indicated.

The government of Nunavut, a territory that is home to most of Canada's Inuit people and which manages or co-manages some 15,000 polar bears, expressed disappointment in the US decision.

"It is unfortunate the (US Government) has decided to disregard facts collected by those who have the greatest contact and longest history with polar bears," Nunavut Premier Paul Okalik said in a statement. "The truth is that polar bear populations are at near record levels."