PIERRE - The U.S. Forest Service issued draft plans on Tuesday that could allow increased poisoning of prairie dogs on national grasslands in Nebraska and South Dakota, including the nation's most successful reintroduction area for endangered black-footed ferrets.

Conservation groups condemned the list of options, arguing it could lead to the destruction of prairie dog colonies and threaten the recovery of black-footed ferrets.

Ranchers in the area want additional poisoning because they contend the continued expansion of the prairie dog population has stripped the public land and adjoining private ranches of grass. The bare dirt has left no grass for cattle, they argue.

The draft environmental impact statement, issued by the Forest Service, is 133 pages long. It lists five options with varying degrees of poisoning of prairie dogs, but the document does not identify any preferred course of action. One option would continue the current management practices.

The Conata Basin just south of Badlands National Park has received the most attention. The prairie dog population has grown substantially in the area during seven years of drought, and it is the site of a successful effort to reintroduce the black-footed ferret, which depends on prairie dogs for food.

For the past two years, the Forest Service has allowed poisoning of prairie dogs on half-mile buffer zones next to private ranches, and the state has poisoned any prairie dogs that venture onto adjacent private land.

The Forest Service is now considering options that include some poisoning of prairie dogs in the interior of the Buffalo Gap National Grasslands. The agency will take public comments on the five management options until July 23.

Don Bright, Forest Service supervisor in Chadron, Neb., has said he hopes to make a final decision on amending the management plan by October.

Charles Kruse of Interior, a rancher who has been a leader in the effort to get more poisoning of prairie dogs, could not comment on the Forest Service draft plans Tuesday because he had not had a chance to read the document.

But Kruse has said the growing prairie dog colony has harmed the land because the rodents have eaten the grass and left bare dirt in many areas. "It's like a moonscape out there," he said last month.

Three conservation groups on Tuesday criticized the Forest Service's list of options, saying three of the five options could reduce prairie dogs to the point that black-footed ferrets could not survive in the Conata Basin.

Defenders of Wildlife, the National Wildlife Federation and the World Wildlife Fund said the Conata Basin is home to half the approximately 500 black-footed ferrets now living in the wild.

Sterling Miller, a biologist for the National Wildlife Federation, said the Forest Service is abandoning its responsibility to maintain healthy wildlife and habitat on public lands. He said he cannot imagine why the Forest Service would spend so much money studying plans to poison more prairie dogs unless it was subject to a lot of political pressure.

American taxpayers have spent millions of dollars on the effort to reintroduce black-footed ferrets into the wild in Conata Basin, Miller said.

"That's the area that's being targeted now for destruction of prairie dogs, and it also will have adverse effects on species that depend on them, most notably black-footed ferrets," Miller told The Associated Press.

Miller said the option that would continue current management practices would be acceptable for ferrets, but he doubts the Forest Service will adopt that option.

"If they were concerned about ferrets, there would be no need to review these plans at all because the existing plan is adequate to protect ferrets and ferret habitat," Miller said.

The conservation groups said that because there are no restrictions on poisoning on private land, the prairie dog colonies on public land should remain large enough to maintain a healthy ecosystem. Swift foxes, burrowing owls, ferruginous hawks and other animals depend on prairie dogs for food or depend on their burrows for shelter, they said.

"With no science to back their claims, the Forest Service is preparing to needlessly eradicate numerous species that make their home in the national grasslands," Steve Forrest of the World Wildlife Fund said in a written statement. "America's grasslands are a significant part of our natural heritage. We should be celebrating and restoring these special places, not destroying them."