BILLINGS, Mont. - A federal appeals court ruled Tuesday that grizzly bears in the Yellowstone region need continued protection under the Endangered Species Act due to the decline of a tree species that serves as a key food source for some of the animals.

The ruling from the 9th U.S. Circuit Court of Appeals blocks the federal government's effort to lift protections on about 600 threatened grizzlies across 19,000 square miles of Montana, Wyoming and Idaho.

Such a move would have turned over management of the animals to state wildlife agencies that could set hunts for grizzlies for the first time in decades.

But Yellowstone's whitebark pine tree stands are fast disappearing because of beetle infestations brought on by a warmer climate. And that means some grizzlies can't get the pine nuts they relied on as a source of protein.

A three-judge 9th Circuit panel said federal wildlife officials wrongly were trying to push past that issue. The U.S. Fish and Wildlife Service had argued grizzlies could adapt and find other food sources.

"Now that this threat has emerged, the Service cannot take a full-speed ahead, damn-the-torpedoes approach to delisting," Judge Richard Tallman wrote.

Judges also were unconvinced that protections could be restored at a later date if the bears' recovery falters: "We reject out of hand any suggestion that the future possibility of relisting a species can operate as a reasonable justification for delisting."

Protections for Yellowstone grizzlies were lifted in 2007 following a costly recovery effort that also has resulted in a sharp increase in bear-human run-ins. Four people have been killed by grizzly bears in Montana and Wyoming over the past two years.

Fish and Wildlife spokesman Chris Tollefson said the ruling was under review.

The agency's grizzly bear coordinator, Chris Servheen, said an appeal was unlikely. He said officials soon would start working on a new proposal to lift protections based on research not available to the 9th Circuit.

Since the case began in 2007 - and despite the loss of whitebark - the grizzly population has continued to expand.

"We're seeing the bears pushing out to where they haven't been in decades, and the density of bears in the center of the ecosystem is very high," Servheen said. "We can provide more information on the whitebark issue as they requested."

Tallman was joined in his opinion by Judge Susan Graber. The 9th Circuit panel's third member, Judge Sidney Thomas of Billings, issued a dissenting opinion. Thomas agreed with the other judges on the whitebark issue. And he said the government also failed to set up adequate plans to protect grizzly bears once they come off the threatened list.

Graber and Tallman said the regulatory framework proposed in 2007 would protect the bears. That part of the case will go back to a lower court for reconsideration.

Grizzly bears were once found across much of the West. Their numbers dwindled rapidly in the late 1800s and early 1900s as intensive hunting and trapping exterminated the animal across more than 98 percent of its historic range in the lower 48 states.

By the time they received protections under the Endangered Species Act across in 1975, as few as 136 bears survived in the Yellowstone region.

A Montana conservation group, the Greater Yellowstone Coalition, challenged the government's decision to lift those protections in a lawsuit four years ago. In 2009, U.S. District Judge Donald Molloy sided with the group in a ruling that restored protections. The government appealed, setting the stage for Tuesday's opinion.

Greater Yellowstone Coalition executive director Mike Clark said the ruling highlighted the impact climate change is having on one of the wildest regions of the country, where 85 percent of high elevation whitebark trees are dead or dying.

"Whitebark is the key food source that has a dramatic effect on whether grizzly bears live or die," said the coalition's attorney, Doug Honnold with EarthJustice. "Since 2007 we've lost a whole lot more whitebark so the situation for grizzly bears is even more dire."

State wildlife agencies, the National Wildlife Federation and the Safari Club had intervened in the case on the side of the federal government.

National Wildlife Federation attorney Thomas France said he was encouraged the 9th Circuit had sided with the government at least on the issue of regulatory protections.

"We feel like the grizzly bear in the greater Yellowstone is a real conservation success story," France said.