ANCHORAGE — A conservation group is again suing the Interior Department for failing to protect what it says is the world's most endangered population of sea otters.

Without action, sea otters in the Aleutian Islands and Alaska Peninsula will become extinct, according to the Arizona-based Center for Biological Diversity, which filed the lawsuit in federal court in Washington, D.C., Wednesday.

The situation is particularly dire in the 1,000-mile-long Aleutian chain in southwest Alaska, where there used to be more than 100,000 sea otters. Now, there could be as few as 2,000, said Brent Plater, a lawyer for the conservation group.

In the past 20 years, the decline in the Aleutians could be more than 95 percent, he said.

"The massive scale of the decline there has made the entire population endangered," Plater said yesterday.

Sea otters in the Alaska Peninsula have not declined as dramatically.

About 90 percent of the world's sea otters live in coastal Alaska.

For years, the Center for Biological Diversity has been waging a legal fight with the Interior Department over sea otters in southwest Alaska. Ultimately, it is the responsibility of Interior Secretary Gale Norton to list them under the federal Endangered Species Act, Plater said.

In 2000, the conservation group became aware of the sharp declines. When the Bush administration refused to move forward to protect them, the center filed a lawsuit Dec. 4, 2003, in federal court in San Francisco.

The federal government responded by issuing a proposed rule Feb. 11, 2004, to protect them. The final rule was to be issued within a year after the proposed rule, but the deadline passed with no action being taken, Plater said.

The Center for Biological Diversity on March 3 sent a letter of notice to the Interior Department and the U.S. Department of Fish and Wildlife that said if no action was taken, the group would sue again.

"They didn't respond to it at all," Plater said.

Now, the group is asking a federal judge in Washington, D.C., to order the Interior Department to issue its final rule. "That will start the process of recovery for sea otters," Plater said.

Fish and Wildlife, which estimates there now are fewer than 42,000 sea otters in southwest Alaska, is recommending that they be listed as threatened. Prior to the decline in the mid-1980s, there were as many as 129,000 sea otters, according to agency estimates.

Douglas Burn, a wildlife biologist for Fish and Wildlife in Anchorage, said the listing means that the species is likely to become endangered in the foreseeable future. The recommendation was sent to the Washington, D.C., office in January.

Burn said there are reasons for the missed deadlines and delays.

"Things have to be reviewed at a variety of levels. Everyone who reviews it has questions and comments," he said. "It is the process. It takes time."

Part of the delay was because of the Selendang Ayu oil spill in the Aleutians in December, Burn said. The soybean freighter was carrying an estimated 442,000 gallons of fuel oil and some diesel when it grounded and broke apart. While roughly 144,000 gallons were removed from the ship, the rest is believed lost.

At least a half dozen sea otters were found dead after the spill.

Plater said the Selendang Ayu illustrates the need to do something now to come up with a recovery plan.

While the reason for the dramatic declines is not known, killer whales are suspected. One theory is that when whales declined in the Bering Sea, killer whales turned to sea lions for food. When sea-lion numbers dropped, the whales turned to sea otters.