ANCHORAGE, Alaska — A federal judge has ordered the Interior Department to decide within 16 days whether polar bears should be listed as a threatened species because of global warming.

U.S. District Judge Claudia Wilken agreed with conservation groups that the department missed a Jan. 9 deadline for a decision. She rejected a government request for a further delay and ordered it to act by May 15.

"Defendants have been in violation of the law requiring them to publish the listing determination for nearly 120 days," the judge, based in Oakland, Calif., wrote in a decision issued late Monday. "Other than the general complexity of finalizing the rule, Defendants offer no specific facts that would justify the delay, much less further delay."

Allowing more time would violate the Endangered Species Act and congressional intent that time was of the essence in listing threatened species, Wilken wrote.

A spokesman for the Interior Department said Tuesday the decision was being reviewed.

"We will evaluate the legal options and will decide the appropriate course of action," said Shane Wolfe in an e-mail statement.

The ruling is a victory for conservation groups that claim the Bush administration has delayed a polar bear decision to avoid addressing global warming and to avoid roadblocks to development such as the transfer of offshore petroleum leases in the Chukchi Sea off Alaska's northwest coast to oil company bidders.

"We hope that this decision marks the end of the Bush administration's delays and denial so that immediate action may be taken to protect polar bears from extinction," Greenpeace representative Melanie Duchin said in a statement.

A decision to list polar bears due to global warming could trigger a recovery plan with consequences beyond Alaska. Opponents fear it would subject new power plants and other development projects to federal review if they generate greenhouse gasses that add to warming in the Arctic.

Assistant Interior Secretary Lyle Laverty has said the department needed until June 30 to complete a legal and policy review of the proposed listing.

Kassie Siegel of the Center for Biological Diversity, the lead author of the petition submitted in 2005, called the judge's order a huge victory, despite not knowing whether polar bears ultimately will be listed.

"It means that whatever political interference going on right now is going to be short-circuited," she said. "The politicians and the bureaucrats in Washington, D.C., are going to have to stop interfering with the decision and get it out the door."

The law requires a decision based on science, she said, and science shows the Arctic is thawing.