ANCHORAGE, Alaska - An environmental group that has pressed the federal government to provide maximum protection for Cook Inlet beluga whales said Thursday it intends to sue.

The issue is over designating critical habitat to help the white whales that swim the waters off of Alaska's largest city recover. The whales were listed as endangered under the federal Endangered Species Act a year ago, meaning they likely are headed toward extinction.

Brendan Cummings, senior attorney for the Center for Biological Diversity, said that the National Oceanic and Atmospheric Administration missed an Oct. 22 deadline to designate critical habitat. The group Thursday filed a 60-day notice of intent to sue.

"Unfortunately, as the beluga continues to decline, NOAA is really dragging its feet in carrying out these necessary measures to protect and ultimately recover the beluga," Cummings said.

Barbara Mahoney, a biologist with the National Marine Fisheries Service in Anchorage, said earlier this month that the critical habitat proposal will be issued this month. She also said a recovery team is being assembled. She did not immediately return a call Thursday for comment.

The state of Alaska opposes the listing and the designation of critical habitat. It has expressed concerns about the potential economic impact the listing will have on development in and around Cook Inlet. Gov. Sean Parnell has said his administration is reviewing the listing.

Critical habitat designation would not stop development in and around Cook Inlet, but would mean that projects needing federal permits, such as the expansion of the port of Anchorage, mining, and gas exploration, would undergo an additional layer of review to make sure those activities do not hurt the animals' chances of recovery.

The Center for Biological Diversity has engaged in a decade-long legal battle over Cook Inlet belugas. A government study released this month found that the animals continue to decline. Their numbers have slipped to 321 belugas - down from an estimated 375, and after two years in which it appeared numbers were stabilizing.

The cause of the decline is not known, but overharvesting by Alaska Natives is believed to have contributed to the downward trend. However, numbers continued to decline even after hunting was sharply curtailed a decade ago. There has been no subsistence hunt for the past three years and none is planned.

The whales are considered a genetically distinct population because they do not mix with the other four beluga groups in Alaska. Those groups are not endangered and number in the thousands.