The Bush administration has 16 days to decide whether polar bears are now an endangered species because of climate change, a California judge ruled today.

The US court handed a victory to three environmental groups that sued to protect polar bears threatened by melting sea ice, rejecting a plea by the government to postpone its decision until June 30.

An agency of the US interior department was supposed to have ruled by January 9 on whether to designate the polar bear an endangered species. But the agency failed to act, angering green activists who attributed the delay to the Bush administration's sale of oil and gas drilling leases near polar bear habitats in Alaska.

The California judge handling the case, Claudia Wilken, ruled that the administration presented "no specific facts that would justify the existing delay, much less further delay".

Rising global temperatures have imperilled the bears by preventing them from hunting beneath the arctic sea ice. Some of the creatures have drowned without sufficient ice for refuge, while others have grown too weak to reproduce.

"These magnificent creatures are in peril, and this administration has no right to walk away from protecting them," Barbara Boxer, Democratic chairwoman of the Senate environment committee, said in a statement on the court decision.

The administration can still decline to list the polar bear as endangered by the May 16 deadline. California officials were forced to sue the Bush administration last year to secure a decision on its proposed carbon emissions caps, but the decision ultimately came down against the state.

If the interior department refuses to afford protections to the polar bear, environmental groups have said they would sue and campaign to force an endangered species listing. The World Wildlife Fund, an animal conservation group, has filmed a public service advert with a TV actor best known for his role on ER, Noah Wyle drawing attention to the polar bears' cause.