Who hates prairie dogs the most? The answer to that Great Plains political question may swing the tight Senate race in South Dakota, determine the fate of the Senate's top Democrat and perhaps even decide which party will control the narrowly divided Senate after next month's election.

To cover his right flank in this conservative state, Senate Minority Leader Thomas A. Daschle has moved on several fronts this year to demonstrate his profound antipathy toward the rodent, which easterners often describe as cute but which generations of rural South Dakotans have shot, poisoned and cussed as a no-good varmint.

He has pressured the Interior Department to drop the black-tailed prairie dog as a candidate for protection as a threatened species, he supports a controversial plan for them to be poisoned this week on federal land, and he says they are "threatening the quality of life in western South Dakota."

Still, his Republican challenger, John Thune, who two years ago came within 524 votes of winning a Senate seat here, claims that Daschle is a "Johnny-come-lately" when it comes to seeing prairie dogs as a menace to South Dakota values.

"They are a symbol for everything that is bad about how the government takes care of its lands," Thune said, adding that Daschle became anti-prairie dog only "after he was boxed into a political corner."

Daschle disagrees, saying, "John is simply wrong. I have been working on behalf of ranchers on this issue for years."

There is a third party in this dogfight: It's the federally protected black-footed ferret, often described as the rarest, most endangered mammal in North America. As much as South Dakota politicians love to hate prairie dogs, the ferrets love to eat them.

Prairie dogs, indeed, are virtually the only creatures that black-footed ferrets do eat. Without lots of prairie dogs, biologists say, ferrets go extinct. And to the extreme annoyance of local ranchers and the politicians who are desperately seeking their vote, the one place in North America where black-footed ferrets are thriving -- as they dine on an expanding population of prairie dogs -- is here in western South Dakota, in the Conata Basin of the Buffalo Gap National Grassland.

The Forest Service, which manages the grassland for grazing, hunting and wildlife conservation, banned shooting and poisoning of prairie dogs here in the mid-1990s. It was part of a costly plan to establish a self-sustaining population of wild ferrets -- and it has been spectacularly successful. Nowhere else, federal officials say, is the black-footed ferret thriving in its ancient prairie habitat.

That success, though, has been accompanied by a prairie dog land grab that infuriates local ranchers. Two years ago, prairie dogs covered about 13,000 acres of federal land in the Conata Basin, according to the Forest Service. Now, they occupy nearly 23,000 acres and are spilling over onto private ranchland.

Having weathered seven years of severe drought that has shrunk their herds and slashed their incomes, ranchers have noisily complained that federal bureaucrats give preference to varmints over hardworking ranch families, who are watching the prairie dogs destroy the grass intended for their cattle.

"Prairie dogs are moving toward our land. It is kind of like a forest fire coming at you," said Charles Kruze, a third-generation rancher and leader of a local anti-prairie-dog coalition.

In this election year, Kruze and other ranchers have been able to bend the ear of Daschle and Thune, as well as Bush administration officials in Washington and nearly every politician in South Dakota. The politicians and officials have all came out in support of the plan to poison prairie dogs on a buffer of federal grassland in the Conata Basin that borders private ranchland.

There is precedent in the Plains states to suggest that even well-known politicians risk electoral oblivion if they neglect populist sentiments regarding local critters. Steve Largent, the former professional football star and high-profile Republican House member from Oklahoma, narrowly lost the governor's race in that state in 2002, at least in part because he supported a proposed ban on cockfighting that outraged rural Oklahomans. They flocked to the polls in higher than normal numbers and made Largent pay for his chicken-loving ways.

Here in southwest South Dakota, two federal officials say that poisoning prairie dogs on federal land may set back ferret recovery. They have been ordered, however, not to say so publicly. "It is election-year craziness," one of them said.

Eight conservation groups sued to halt the poisoning. They argued that the federal government was ignoring its own rules, which make ferrets (and the prairie dogs they eat) the top priority in managing the Conata Basin. But a federal judge in Denver presided on Wednesday over a negotiated settlement of the suit that allows poisoning to start next week, though on less acreage than the ranchers had demanded.

Some biologists who study prairie dogs say politicians are overreacting to periodic drought.

"It's disgusting," said John L. Hoogland, a professor of biology at the University of Maryland's Center for Environmental Science's Appalachian Laboratory in Frostburg. He said 20 years of research work on ferrets is being placed "in jeopardy for politics -- for a temporary drought and on lands that don't belong to the ranchers anyway."

Research by Hoogland has established the prairie dog as a "keystone species" in the Great Plains, a protein source that hundreds of animals depend on.

Except in severe drought, prairie dogs can also have a symbiotic relationship with cattle, said Jim Detling, a University of Colorado biology professor. For thousands of years, prairie dogs depended on buffalo to knock down prairie grass so the dogs could stand up on their hind legs and see who might be coming to eat them. They have an elaborate system of barks to sound alarms.

Cattle also like to hang out with prairie dogs, Detling said.

"There is a lot of anecdotal evidence that cattle will preferentially move to prairie dog areas, especially in the type of grasslands you have in South Dakota," he said, noting that while prairie dogs reduce forage, what remains has more protein.

There is a limit, though, to the benefits of this relationship. "I can fully understand why a rancher wouldn't want prairie dogs to get out of control on his pastures," Detling said.

It was 200 years ago last month that the Lewis and Clark expedition first saw a prairie dog, which William Clark called a "barking squirrel." To show their boss, President Thomas Jefferson, the richness of the fauna in the West, the explorers shipped a live one back to the White House. Jefferson kept it for several months, describing it in a letter as "a most harmless and tame creature."

Over the past two centuries, however, the charms of the prairie dog have eluded ranchers and politicians in the Plains states. Prairie dog numbers, estimated in the billions before settlement, collapsed from widespread poisoning, which pushed some species to the brink of extinction.

In a move that outraged ranchers, federal officials named the black-tailed prairie dog in the 1990s as a candidate for protection under the Endangered Species Act. It took until this August, with the South Dakota Senate race locked in what polls suggest is a dead heat, for such protection to be dealt a final deathblow when the move to give the prairie dog protected status was abandoned.

Meanwhile, Daschle, Thune and the Bush administration continue to elbow each other as they take credit for toughness on the dogs.

"It is one thing to spout political rhetoric and another thing to get something done -- that's the difference between a leader and a follower," said Daschle, who noted that in May he called a meeting with Interior Secretary Gale A. Norton and "pressed" her to remove the black-tailed prairie dog from the threatened list.

When Norton did make the announcement, though, she said nothing about Daschle. Instead, she thanked Thune for his "leadership" on prairie dogs.

Moves to protect the prairie dog have created an election issue in South Dakota because ranchers see the rodent as a threat to grazing.Charles Kruze and other ranchers favor poisoning prairie dogs in parts of the Buffalo Gap National Grassland, where their colonies are expanding. Thomas A. Daschle says the animals are "threatening the quality of life in western South Dakota."Republican John Thune says the issue symbolizes "everything that is bad about how the government takes care of its lands."