Federal officials on Tuesday proposed designating an area more than twice the size of California as critical habitat to protect ringed seals, animals dependent on dwindling Arctic sea ice and snow for their survival.

About 350,000 square miles of icy marine territory in the Beaufort Sea off northern Alaska, the Chukchi Sea off northwestern Alaska and the northern Bering Sea off the state's western coast would be designated as critical ringed-seal habitat under provisions of the Endangered Species Act, according to the rule proposed by the National Oceanic and Atmospheric Administration's Fisheries Service.

If the rule is adopted as proposed, the protected zone for ringed seals would be the nation's most vast critical habitat. For now, the critical habitat designated in July for threatened loggerhead sea turtles -- an estimated 317,544 square miles of beaches and marine waters in the Atlantic Ocean and Gulf of Mexico, according to NOAA -- is the largest in the nation.

Ringed seals, listed in December of 2012 as threatened, depend on sea ice and the snow atop it for survival and reproduction. They use snow caves on the sea ice to nurse and protect their pups, and they use floating sea ice for molting, breeding and raising their young. The seals are now imperiled by changing Arctic conditions -- diminished sea ice in the spring and fall and deteriorating snow cover, partly the result of winter rains that have become more common, according to scientists from NOAA and other organizations.

The Endangered Species Act requires identification and protection of critical habitat used by listed species. According to the law, any activity permitted, funded or conducted by the agency within designated critical habitat must be vetted with all applicable federal agencies to make sure those activities do not result in harm to the listed species.

The Beaufort, Chukchi and Bering sea areas proposed for designation are vital to the survival of the ice- and snow-dependent seals, NOAA officials said.

"After reviewing the best available information, our scientists identified the habitat features that are essential for sustaining Arctic ringed seals -- a species that is likely to become endangered in the foreseeable future due to climate change," James Balsinger, NOAA Fisheries' Alaska regional administrator, said in a statement.

Environmentalists were pleased with the proposal.

"We're thrilled that the ringed seals are getting the habitat protections they so desperately need as their sea-ice home melts beneath them," Shaye Wolf, climate science director for the Center for Biological Diversity, said in a statement. The center, which has been advocating for listing of all Alaska ice seals, filed the original 2008 listing petition, followed by a lawsuit against the Obama administration for alleged foot-dragging.

But Sen. Lisa Murkowski said the proposal, if enacted, would hamper oil and gas drilling and other economic activities -- and added that she believed listing of the ringed seals might not be warranted.

"This is an unprecedented attempt to place restrictions on a larger-than-Texas-sized area of water surrounding our state," she said in a news release. "I remain skeptical that the listing of ringed seals based on a 100 year weather projection was justified, and I am concerned that this designation would severely impact any economic development from Northwest all the way to our border with Canada."

The proposed critical habitat designation is subject to a 90-day public comment period. The time needed to enact a final rule will depend in part on how many comments are received, said Julie Speegle, a NOAA spokeswoman in Juneau.

Establishment of critical habitat for another threatened species dependent on dwindling Arctic sea ice, the polar bear, ran into a legal roadblock.

The Fish and Wildlife Service in 2010 designated polar bear critical habitat comprising 187,157 square miles of Alaska Arctic marine and coastal territory, a little more than half the total area proposed as ringed seal critical habitat. Oil industry groups, the North Slope Borough, Native corporations and the state of Alaska sued to block that designation.

U.S. District Court Judge Ralph Beistline on Jan. 10, 2013 voided the polar bear critical habitat designation, which he said "went too far and was too extensive." Beistline ordered the agency to rewrite its critical habitat designation.