BILLINGS, Mont. – A federal judge has restored endangered species protections for gray wolves in the Northern Rockies, derailing plans by three states to hold public wolf hunts in the fall.

U.S. District Judge Donald Molloy in Missoula granted a preliminary injunction late Friday restoring protections for the wolves in Montana, Wyoming and Idaho.

Molloy will eventually decide whether the injunction should be permanent. That would force the government back to the beginning in its effort to pass management of the animals to the states.

An estimated 2,000 wolves now roam the Northern Rockies, according to the latest estimate by the U.S. Fish and Wildlife Service. They were removed from the endangered species list in March, following a decade-long restoration effort.

Environmentalists sued to overturn the decision, arguing wolf numbers would plummet if hunting were allowed. They sought the injunction in the hopes of stopping the hunts and allowing the wolf population to continue expanding.

“There were fall hunts scheduled that would call for perhaps as many as 500 wolves to be killed. We're delighted those wolves will be saved,” said attorney Doug Honnold with Earthjustice, who had argued the case before Molloy on behalf of 12 environmental groups.

In his ruling, Molloy said the federal government had not met its standard for wolf recovery, including interbreeding of wolves between the three states to ensure healthy genetics.

“Genetic exchange has not taken place,” Molloy wrote in the 40-page decision.

He said hunting and state laws allowing the killing of wolves for livestock attacks would likely “eliminate any chance for genetic exchange to occur.”

The federal biologist who led the wolf restoration program, Ed Bangs, defended the decision to delist wolves as “a very biologically sound package.”

“The kind of hunting proposed by the states wouldn't threaten the wolf population,” Bangs said Friday. “We felt the science was rock solid and that the delisting was warranted.”

Bangs said government attorneys were reviewing Molloy's court order and would decide next week whether to appeal to the 9th U.S. Circuit Court of Appeals.

Federal and state officials had argued killing some wolves would not endanger the overall population – as long as numbers did not dip below 300 wolves. With increasing conflicts between wolves and livestock, they said public hunts were crucial to keeping the predators' population in check.

But Molloy wrote the U.S. Fish and Wildlife Service signed off on state hunting plans only after reversing its prior stance that state laws – particularly in Wyoming – were inadequate.

In 2004, the federal agency rejected Wyoming's wolf management plan because it allowed wolves to be shot on sight across a majority of the state. When the boundaries of that “predator zone” changed last year, the shoot-on-sight provision remained.

“Armed with the same information, the Service flip-flopped without explanation,” Molloy wrote.

More than 100 wolves have been killed since the states took over management of the animals in March, according to environmental groups that drew their tally from state wolf management reports.

However, even prior to the states gaining control, government wildlife agents had killed the predators at a steady pace. More than 700 had been killed in response to livestock conflicts through the end of 2007.

State officials and representatives of the livestock industry expressed disappointment with Molloy's ruling.

“The state of Idaho has developed a sound and responsible plan for managing wolves to maintain a sustainable population. We will be examining the decision and carefully considering the next step,” said Mark Warbis, a spokesman for Idaho Gov. C.L. “Butch” Otter.

Wyoming Gov. David Freudenthal said he was not surprised with Friday's ruling, given Molloy had earlier said he was “unwilling to risk more deaths (of wolves).”

Jim Magagna, executive vice president of the Wyoming Stockgrowers Association, said the number of wolves killed under state management was minimal.

“If a species that's recovered to the extent that the wolves have cannot be delisted, it confirms to me that the Endangered Species Act is truly broken,” Magagna said.

The National Wildlife Federation had stayed out of the environmentalists' lawsuit, saying it could distract from efforts to protect other, more imperiled species.

But for the plaintiffs in the case, Friday's ruling marked a major victory.

“The wolf slaughter is halted,” said Michael Robinson with the Center for Biological Diversity. “We're elated.”

Associated Press writers Matt Joyce in Cheyenne, Wyo., and John Miller in Boise, Idaho, contributed to this report.