Most wolves in the continental United States soon will be off federal assistance.

For more than 300 years, trappers and settlers did their best to exterminate wolves, for their pelts and to protect livestock. They were so successful that only a few hundred gray wolves were left in the lower 48 states when they were listed as an endangered species in 1973.

Now the wolves are back, with roughly 6,000 in the contiguous United States and 7,700 to 11,200 in Alaska. The Obama administration has declared all but two small populations — Mexican gray wolves in New Mexico and Arizona and red wolves in North Carolina — fully recovered. On Oct. 1, Wyoming will become the fifth state with a significant wolf population to legalize hunting.

Fish and Wildlife Service Director Dan Ashe called the wolf comeback "a great success," but it means that wolves are now fair game, and he noted that not everyone likes the idea of killing them.

"When you look at our friends in the environmental movement, there are a lot of people out there who just don't like the idea of animals being shot," Ashe said. "I understand that, but if you look at the Endangered Species Act, it's not an animal-protection act. It's a law designed to prevent the extinction of a species."

But how many wolves are enough?

The Fish and Wildlife Service approved plans in Montana, Idaho and Wyoming that require them to maintain a minimum of 450 adults and 45 breeding pairs of wolves. The population now stands at 1,774 adults and 109 breeding pairs, and the agency projects that hunting will bring the number of adults down to about 1,000.

"It's hard to fathom that you can be deserving of federal protection under the Endangered Species Act on September 30 and on October 1 be open fire," said Jamie Rappaport Clark, president of Defenders of Wildlife.

Ken McDonald, chief of wildlife at the Montana Fish, Wildlife and Parks Department, said the state aims to keep around 400 gray wolves on the landscape to minimize conflict with ranchers and hunters, who have complained when wolves attacked either livestock or deer and elk.

Montana's wolf population actually rose 15 percent after last year's hunting season, to a total of at least 650, prompting the state to allow unlimited hunting of wolves between Sept. 1 and Feb. 28. It also has allowed trapping for the first time.

"Despite the hype, we didn't go out and wipe them out at the first opportunity," said McDonald, adding that wildlife managers are seeking "a balance" in which wolves exist but don't threaten cattle or big-game populations.

Scientists say that wolves play a key role in the ecosystem. Aspen trees in Yellowstone National Park suffered in the decades when wolves were absent, and began to thrive when wolves came back and kept leaf-eating elk in check. Since wolves were reintroduced there in the mid-90s, browsing on the tallest aspens researchers surveyed declined by more than 75 percent, according to Oregon State University ecologist William Ripple. This produced other ripple effects, including cooler streams shaded by trees and more vibrant beaver and bison populations that had more plants to eat.

"Rather than just maintaining enough wolves to keep them from going extinct, what researchers and managers should consider is how many wolves would it take for them to be effective at influencing the ecosystem," Ripple said. "What does it take to keep the prey populations in check, in order to maintain healthy plant communities?"

But it is unclear how much tolerance some local residents have for wolves, especially in the northern Rockies and the Southwest. Wolves have made gains in Michigan, Minnesota and Wisconsin without sparking much controversy. There are more than 4,000 in those states, with an estimated 2,921 in Minnesota alone.

But after a Forest Service employee in Idaho posted a photo of himself with a wolf that he had trapped and shot, wolf activists erupted in outrage. And last week several groups filed notice of their intent to sue, challenging Wyoming's right to manage wolves on grounds including that its plan would allow for wolves to be treated as predators — and shot on sight — in most of the state.

Noah Greenwald, endangered species director for the advocacy group Center for Biological Diversity, said that federal officials have declared wolves recovered not because they had finished the job but "because they want to avoid the political controversy that wolves generate."

Wyoming Game and Fish Department spokesman Eric Keszler said there are "hardly any wolves" living in an area where they can be shot on sight, since the vast majority of the state's 328 wolves live in the northwestern part of the state. The federal government will continue to oversee the wolves living in Wyoming's section of Yellowstone, and the state will treat most wolves as trophy game, which requires a license.

"It's not going to be the mass slaughter of wolves that some people talk about," Keszler said.

Neil Thagard, a big-game hunter based in Cody, Wyo., who serves as Western outreach director for the Theodore Roosevelt Conservation Partnership, said people should let the wildlife managers decide the appropriate level for wolves and allow them to use the tools they need, including hunting. He added that many of his fellow hunters exaggerate wolves' impact on both livestock and game.

Ashe acknowledged that the Fish and Wildlife Service had not figured out how to overcome the fact than some people in the rural West view wolves more as a threat than an asset. "If I could wave a magic wand and go back to the early '90s, I think we had the biology right, but we didn't build the social context for wolf conservation before we put wolves out on the landscape," he said.

He added that his agency for the next five years will monitor how the wolves are faring.

In the Southwest, the road to recovery was even more daunting. In 1998, federal authorities released 11 Mexican gray wolves into the Arizona wilderness, and 14 years later there are only 58.

Chris Bagnoli, interagency field team leader for the Arizona Game and Fish Department's Mexican Wolf Reintroduction Project, ticked off a long list of obstacles to the Mexican wolf's recovery: ineffective management, illegal wolf kills, effects on livestock and game, the population's genetic viability and health, and human safety. The New Mexico Game and Fish Department, which declined to comment, stopped working with federal officials to help the Mexican wolf in June 2011.

While Defenders of Wildlife has financed several programs aimed at helping cattle ranchers coexist with wolves — hiring range riders, putting up fences and compensating for lost cattle — many ranchers are losing patience with the reintroduction program.

Patrick Bray, executive director of the Arizona Cattle Grower's Association, said the presence of wolves increases costs even when they don't kill livestock, by making cattle nervous and forcing ranchers to move their herds frequently.

"We're not going to be comfortable with an expanded range moving forward, with an expanded program, until we figure out how to make the existing program work," Bray said.

By the end of the month, Fish and Wildlife will have to determine if the Mexican gray wolf is a subspecies of the gray wolf, rather than a "distinct population segment." Colorado and Utah are fighting the subspecies designation on the grounds that it could lead to Mexican wolves expanding their range into their states. And wolves that wander out of their established areas — into the Pacific Northwest, for example — are still protected as endangered under federal law.

Defenders of Wildlife's Clark, who helped release wolves raised in captivity into an enclosure in Arizona's Apache National Forest 14 years ago when she headed the Fish and Wildlife Service, said the thrill she's felt seeing wolf populations rebound has been tempered by her sorrow as the animals have failed to gain social acceptance. Wolf watching has become a tourist draw in Yellowstone and has spawned many "tchotchkes" in the concession stores, she noted, but beyond the park's borders there are clear limits on how many wolves will be tolerated.

A century ago, Americans fought wolves for dominance of the landscape and "we won." Now, she added, "We have to find a way to balance the needs of nature with the needs of humans."