The suit, filed in U.S. District Court in San Francisco on Thursday, asks the Interior Department to make an initial ruling on a petition to bestow the broad federal protection of the Endangered Species Act upon polar bears by designating them as "threatened."

An "endangered" species is one that is in danger of extinction throughout all or a significant portion of its range, according to the U.S. Fish and Wildlife Service's Web site (http://www.fws.gov). A "threatened" species is likely to become endangered in the foreseeable future, according to the agency.

The lawsuit was filed by the Center for Biological Diversity, the Natural Resources Defense Council and Greenpeace, which say the department should have ruled on its petition within 90 days of its filing in February.

If the suit is successful, there will be two more steps, each of which can take up to a year, before polar bears could be officially listed as threatened.

The groups argue that rising global temperatures endangers polar bears by melting the ice floes on which the giant predators prowl and hunt.

Kassie Siegel, climate director for the Center for Biological Diversity, said the group's petition on polar bears was bolstered by a report this week from the U.S. Minerals Management Service detailing the deaths of four polar bears that drowned in September 2004.

"As global warming continues, more bears are going to die. This is very predictable, it's common sense," Siegel said. "Their habitat is sea ice. They don't hunt from land, they don't hunt from water. They can't survive if their habitat disappears."

A spokesman for the Interior Department did not return a call seeking comment.