Washington —- Interior Secretary Dirk Kempthorne announced Wednesday that his agency will list the polar bear as threatened under the Endangered Species Act, a decision that could cast the bears as the enduring symbol of the effects of global warming.

But Kempthorne also warned that the listing "will not stop global climate change or prevent sea ice from melting" and that he will not permit the Endangered Species Act to be used as a tool for changing U.S. policy on global warming or greenhouse gas emissions.

Kempthorne's decision, forced by federal courts, is his first Endangered Species Act listing since joining President Bush's Cabinet in 2006 and the first for an animal that's losing its habitat to global warming. Polar bears use sea ice as a platform to trap their primary prey, seals.

Scientists with the U.S. Geological Survey predicted in September that only a small proportion of the existing 25,000 of the world's polar bears would remain in the islands of the Canadian Arctic by midcentury. The study found that two-thirds of the world's polar bears will have disappeared, mostly along the coasts of Alaska and Russia.

But Kempthorne said there is simply no scientific way to connect specific greenhouse gas emissions from specific smokestacks to the harm of a species or its habitat.

Kempthorne on Wednesday had the director of the U.S. Fish and Wildlife Service issue a memo that says the existing science doesn't make such a connection.

As a result, when new power plants and other emitters of greenhouse gases seek permission to operate, the Fish and Wildlife Service can't use the polar bear listing as a reason to deny a permit.

The Interior Department also issued a rule intended to ensure continued oil and gas development.

"This rule, effective immediately, will ensure the protection of the bear while allowing us to continue to develop our natural resources in the arctic region in an environmentally sound way," Kempthorne said.