Looking at the diminutive flat-tailed horned lizard, you wouldn't think it would cause much of a problem for anyone.

But the scaly desert reptile, which rarely grows longer than 4 inches, has been at the forefront of an enormous back-and-forth legal battle between federal officials and environmental interest groups seeking broader protections for the animal.

The Tucson-based Center for Biological Diversity, representing a group of activists and scientists, filed suit Thursday in a Tucson federal court alleging U.S. Interior Secretary Gale Norton and the Bush administration have denied the lizard proper protection under the Endangered Species Act.

The suit is attempting to reverse a January ruling by the U.S. Fish and Wildlife Service that the species is not threatened.

"This particular species has been a lightning rod for controversy and litigation," said U.S. Fish and Wildlife Service spokeswoman Jane Hendron from the service's Carlsbad office.

Hendron said her department had not read the lawsuit but she said she understands it is challenging the department's analysis of habitats, populations and impacts to the lizard completed this January showing the species does not qualify for ESA protections.

Fish and Wildlife first proposed listing the species under the ESA in 1993, Hendron said, but withdrew its proposal in 1997 with the finalization of a management strategy for the animal's habitat.

The withdrawal was challenged in court later that year by conservation groups. A federal court ordered the service to reinstate the 1993 rule to list the lizard and make a final listing determination.

The CBD's lawsuit challenges that final ruling in January, Hendron said.

The animal's primary habitat, portions of the Sonoran Desert, include public land in Imperial, Riverside and San Diego counties, Arizona and Baja California.

"(President) Bush's unjustified and illegal denial of protection for the lizard must be reversed," said Daniel Patterson, a desert ecologist with CBD.

The latest suit is an attempt by environmentalists to shut off access to public lands completely, according to off-road enthusiasts.

"I consider myself an environmentalist," said Roy Denner, president of the Off-Road Business Association, based in Lakeside.

"If there was a road where these animals were being run over on all the time, I'd want to see it closed. But I've never seen a dead flat-tailed horned lizard in my life."

Denner, on the U.S. Bureau of Land Management's Desert Advisory Council, said the government's studies, as well as research by an outside herpetologist hired by the group, shows the species' habitat is not endangered.

"The CBD has a list of species they are just going down in order to close off access to areas," Denner said. "I believe we have balance with the current approach. If we go down they path they want, everybody loses."

Environmentalists claim threats to the lizard include crops, cities, off-road vehicles and the reduction of the animal's habitat to urban sprawl.

Citing decline of the species in areas such as the Coachella Valley, University of California biologist Al Muth said the decision to not protect the species is "ludicrous."

"This smells of politics more than biology," Muth said.

Activists also cite pesticide drift from agriculture as a danger to harvester ants, which are the primary food of the lizard.

Patterson points to a pending Department of Interior decision to open 50,000 protected acres of public land in the Algodones Dunes to off-road use as an example of "deadly management" for the species habitat.

Imperial County Supervisor Wally Leimgruber, who's district includes the Algodones Dunes, said he is disappointed by the lawsuit.

"The (CBD's) intent is to close the Desert Southwest to public access," Leimgruber said. "I am disappointed in their actions, but will continue to work to keep our public lands open to the public."

Leimgruber said around 95 percent of desert lands never see a human footprint and drought conditions and natural impacts affect species more than hiking, OHV use and other human impacts.

"Studies continue to show that responsible access to these lands don't adversely impact these animals," Leimgruber said.