A conservation group went to court Wednesday to force the federal government to consider adding Pacific walrus to the list of threatened species.

The Center for Biological Diversity sued the U.S. Fish and Wildlife Service and Interior Secretary Dirk Kempthorne for failing to act on a petition seeking protection for walrus under the Endangered Species Act.

Walrus are threatened by global warming that melts Arctic sea ice, according to the group, which was one of the parties that successfully petitioned to list polar bears as threatened. The group also has filed petitions to protect Arctic seals.

The walrus petition was filed in February. The Fish and Wildlife Service was required by law to decide within 90 days, on May 8, whether the petition had merit, triggering a more thorough review and a preliminary decision after 12 months.

Center for Biological Diversity attorney Rebecca Noblin of Anchorage said delays will harm walrus.

"Every day that goes by without protecting the walrus, we're emitting more greenhouse gases, accelerating the ice melt," she said.

"In addition to the climate change, the other main threat is oil and gas development that continues to go forward without any consultation regarding walrus," she said.

Fish and Wildlife spokesman Bruce Woods said Wednesday the agency anticipates deciding on the petition but has limited resources. Agency decisions on endangered species listings are driven by litigation, he said, forcing the agency to rank actions by court order rather than species need.

Warming is blamed for Arctic sea ice shrinking to record lows.

The National Snow and Ice Data Center said summer sea ice in 2008 reached the second-lowest level, 1.74 million square miles, since satellite monitoring began in 1979. The loss was exceeded only by the 1.65 million square miles in 2007.

Like polar bears, listed as a threatened species by Kempthorne in May, walrus depend on sea ice to breed and forage.

Walrus dive from ice over the shallow outer continental shelf in search of clams and other benthic creatures. Females and their young traditionally use ice as a moving diving platform, riding it north like a conveyor belt as it recedes in spring and summer, first in the northern Bering Sea, then into the Chukchi Sea off Alaska's northwest coast.

Sea ice in the Chukchi Sea, shared with the Russian Far East, for the last two years receded well beyond the outer continental shelf over water too deep for walruses to dive to reach clams. In fall 2007, herds congregated on Alaska and Siberia shores until ice re-formed.

According to the Center for Biological Diversity, warming sea temperatures and sea ice loss may also be reducing walrus prey at the bottom of the ocean.

The group also hopes a listing could slow plans for offshore petroleum development. Oil companies in February bid on 2.7 million acres in the Chukchi Sea. Other lease sales are planned.

Noblin said the group was required to give 60 days notice of intent to sue but also waited to give the agency ample time to meet its obligation. She said it's clear the agency will not meet the 12-month deadline in February for a draft rule on the proposed listing.

The Fish and Wildlife Service has nearly completed a population count of walrus coordinated with Russian counterparts.

The challenge has been "trying to finish grinding out the numbers between two languages and two divergent sets of scientists" to besure they're comparing apples to apples and not "fruit salad," Woods said.

The numbers are anticipated no later than January and possibly this month, he said.