DENVER -- Here in Colorado, the hottest political issue of the day may not be the war in Iraq or the out-of-control federal budget, but rather the plight of a tiny mouse. Back in 1998, a frisky eight-inch rodent known as the Preble's meadow jumping mouse gained protective status under the 1973 Endangered Species Act (ESA). What has Coloradans hot under the collar is that some 31,000 acres of local government and privately owned land in the state and stretching into Wyoming -- an area larger than the District of Columbia -- was essentially quarantined from all development so as not to disrupt the mouse's natural habitat. Even the Fish and Wildlife Service concedes that the cost to these land owners could reach $183 million.

What we have here is arguably the most contentious dispute over the economic impact of the ESA since the famous early-'90s clash between the timber industry and the environmentalist lobby over the "endangered" listing of the spotted owl in the Northwest. That dispute eventually forced the closure of nearly 200 mills and the loss of thousands of jobs. Last week the war over the fate of the Preble's mouse escalated when a coalition of enraged homeowners, developers and farmers petitioned the Department of the Interior to have the mouse immediately delisted as "endangered" because of reliance on faulty data.

The property-rights coalition would seem to have a fairly persuasive case based on the latest research on the mouse. It turns out that not only is the mouse not endangered, it isn't even a unique species.

The man who is almost singlehandedly responsible for exposing the truth about the Preble's mouse is Rob Roy Ramey, a biologist and lifelong conservationist, who used to serve as a curator at the Denver Museum of Nature and Science. Mr. Ramey's research -- published last year in the peer-reviewed journal Animal Conservation -- concluded that the Preble's mouse "is not a valid subspecies based on physical features and genetics." The scientist who conducted the original research classifying Preble's as unique now agrees with Mr. Ramey's assessment. Even scientists who defend extending the mouse's "endangered" status admit that it is 99.5% genetically similar to other strains of mice.

Nor is the mouse on the road to extinction. "The more people look for these mice, the more they find. Every time scientists do a new count, we find more of the Preble's mouse," Mr. Ramey says. It's now been found inhabiting twice as many distinct areas as once thought. These are mice, after all, and the one thing rodents are proficient at is breeding. The full species of the meadow jumping mouse, far from being rare, can be found over half the land area of North America.

"The federal government has effectively shut off tens of millions of dollars of economic development," complains coalition spokesman Kent Holsinger, "based on saving a species that we now know doesn't even exist." But green groups and Department of Interior bureaucrats, who regard the ESA as a sacred pact -- the modern-day equivalent of Noah's Ark, as former Interior Secretary Bruce Babbitt called it -- pledge to fight any change in status.

Not surprisingly, Mr. Ramey has been accused of being "dishonest," a "whore for industry" and a "shill for the Bush administration." Under intense political pressure from environmental activists, he was removed from his curator's job at the museum. "I've been nearly stampeded by a herd of agitated elephants in Africa and suspended from some of the highest cliffs in North America, but nothing prepared me for the viciousness of the attacks from the environmentalist lobby," he tells me.

Meanwhile, the Preble's mouse continues to impose huge costs on local communities. One water district in Colorado was recently required to build two tunnels for the mice under a man-made pond to spare the critters the inconvenience of having to scurry around it. Regulators asked local officials if it would be feasible to grow grass in the tunnels for the mice, which was only slightly less absurd than padding the mouse thoroughfares with red carpet. The extra cost to the water project to make it mouse-friendly? More than $1 million. The Fish and Wildlife Service also has the authority to assess penalties on property owners if they even inadvertently spoil mouse habitat. Owners can even be fined if their cats do what cats do: chase and apprehend mice.

A comprehensive 2003 survey found that more than one in four land owners impacted by the Preble's mouse regulation "admitted to actively degrading habitat following the species listing in 1998." This is often precisely what happens in these situations: Because most of 1,500 or so species that have been listed as threatened since 1972 are anything but, people have no respect for the designation and attempt to force the species away from their land. They call it "shoot 'em, shovel 'em and shut up." For truly endangered species, the ESA is a disaster.

Many individuals have been so strong-armed by federal bureaucrats that they have come to believe -- with good reason -- that the original and widely supported intent of the ESA has been subverted into a back-door means to slam the brakes on economic development. "It's a cost-free way for the government and the greens to impose land-use control on property owners," says R.J. Smith, an ESA expert at the Competitive Enterprise Institute.

Therein lies the crux of the problem. The law tries to achieve the societal policy goal of saving species from extinction by imposing all of the costs on a hapless few. House Resources Committee Chairman Richard Pombo has sensibly proposed reforms that allow landowners to get fair compensation from the government if their land is depressed in value due to a wetlands or endangered species designation. That seems equitable: If society wants to preserve habitat for the common good, then the cost should be borne by all taxpayers, not individual landowners, who would no longer regard endangered species as an economic plague.

If anything good can come out of the Preble's mouse fiasco in Colorado, it will be that it has awakened Congress to the reality that the ESA isn't just failing property owners but the very irreplaceable species it was designed to protect.

Mr. Moore is a member of The Wall Street Journal's editorial board.