BILLINGS, Mont. (AP) — A proposal to lift federal protections for gray wolves across most of the U.S. suffered a significant setback Friday as an independent review panel said the government is relying on unsettled science to make its case.

Federal wildlife officials want to remove the animals from the endangered species list across the Lower 48 states, except for a small population in the Southwest.

The five-member U.S. Fish and Wildlife Service peer-review panel was tasked with reviewing the government's claim that the Northeast and Midwest were home to a separate species, the eastern wolf.

If the government were right, that would make gray wolf recovery unnecessary in those areas.

But the peer reviewers concluded unanimously that the scientific research cited by the government was insufficient.

That could make it difficult for federal officials to stick with their proposal as it now stands, further protracting the emotionally charged debate over what parts of the U.S. are suitable for the predators.

"The process was clean and the results were unequivocal," said panel member Steven Courtney, a scientist at the National Center for Ecological Analysis and Synthesis at the University of California in Santa Barbara. "The science used by the Fish and wildlife service concerning genetics and taxonomy of wolves was preliminary and currently not the best available science."

Wolves were added to the endangered species list in 1975 after being exterminated last century across most of the Lower 48 states under government-sponsored trapping and poisoning programs.

Hunting for wolves already is allowed for roughly 5,000 wolves in the Northern Rockies and Great Lakes, where protections were lifted in 2011. More than 900 of the animals have been shot or caught by trappers in the two regions during this winter's hunting season.

A struggling population of several dozen Mexican gray wolves in the desert Southwest would remain on the endangered list under the government's plan. The Southeast is home to a separate species, the red wolf, which remains highly endangered.

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The release of the peer review findings opens another round of public input on a proposal that has received more one million comments.

"Obviously we do take the comments from peer reviewers very seriously and we need to take those into account," Fish and Wildlife Service spokesman Chris Tollefson said.

The Fish and Wildlife Service already faced fervent opposition to its plan from some scientists, wildlife advocates and members of Congress. They've argued that protections should remain in place given that vast areas of potentially suitable wolf habitat remain unoccupied in the southern Rocky Mountains, along the West Coast and in the Northeast.

Carlos Carroll, a wolf researcher at the Klamath Center for Conservation Research in Orleans, Calif., said the problems highlighted by the peer-review panel had been raised previously by others. He said he hoped they would now get more attention from wildlife officials.

"This gives them a chance to re-evaluate their strategy and say it's time to listen to the science," Carroll said.

The ranking Democrat on the U.S. House Natural Resources Committee, Oregon Rep. Peter DeFazio, on Friday called on the Fish and Wildlife Service to rescind its proposal in light of the peer review.

But feelings run strong on both sides of the issue. Many Republican lawmakers, agricultural interests and hunting groups have pushed equally hard for jurisdiction over wolves to be passed to states so they could manage the population through annual harvests.

Those efforts have been motivated in large part by wolf attacks on livestock and big game herds in areas where the predators have recovered.

David Allen, with the Rocky Mountain Elk Foundation, said that after several years of hunting, it's clear the harvests are not driving down the wolf population too aggressively.

An earlier peer-review panel charged with reviewing the delisting proposal was dissolved last summer, after criticisms arose when three scientists who had been critical of the government's wolf plan were told they couldn't serve.

One of the three — Robert Wayne at the University of California Los Angeles — was later named to the panel that came up with Friday's report.

Officials had aimed for a final decision on the matter this summer. That's now uncertain after delays in the peer review and time lost to the federal government shutdown in the fall.

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Associated Press Writer Jeff Barnard in Grants Pass, Ore., contributed to this report.