Executives of the Summa Corporation were seeing dollar signs in the dry Nevada earth last August as they broke ground for Summerlin, a multibillion-dollar development of 22,000 acres in northwest Las Vegas. But there was one small hitch: a few dusty brown tortoises slowly inching away into the empty Mojave as Summa's giant bulldozers rolled onto the site.

If Summa's officials didn't pay any mind to the reptiles that day, they do now. Last month the U.S. Fish & Wildlife Service declared the Mojave Desert tortoise a threatened species, thus drastically restricting construction or other disturbance of the creatures' territory in a 25,000-square-mile area of Nevada, Arizona, California and Utah.

The "threatened" designation, one notch down from "endangered" in the hierarchy of protection, came in response to a severe crisis for the reptiles. In the western Mojave region alone 70 percent of the creatures—which may grow 14 inches long and live to be 80—have been lost since 1980. Within the last three years a respiratory disease has wiped out some 40,000 of them, and many survivors have been extinguished by housing, off-road vehicles and grazing cattle.

Such depredations also carry implications beyond the fate of one lowly tortoise. Wildlife biologist Kristin Berry, a leader in the tortoise crusade, says the decline of the 10-million-year-old reptile prefigures a similar fate for other forms of life. "These tortoises are an 'indicator species,' like canaries that are sent down mine shafts to test for poisonous gases," Berry explains. "They live close to the food base. If they can't make it, neither can a lot of other animals."

Many Mojave residents, though, are furious that one ungainly species can get in the way of their livelihoods. They cite a critical shortage of housing and services for the growing Las Vegas work force and say that steeper housing costs are sure to follow. Still, some compromises have been reached, Summa and nine other developers have agreed to donate $2.5 million toward a tortoise research and conservation center in return for permission to build on 7,000 approved acres. Some 30,000 single-family units are envisioned for the land, now the home of 400 to 800 tortoises. Further development on tortoise habitat must await a conservation plan, which may take three years.

In California, three popular off-road desert races have been scuttled as a result of an earlier emergency ruling on behalf of the reptiles, and cattle and sheep ranchers may have to modify grazing practices. "The preservationists are using the Endangered Species Act to eliminate multiple use on federal lands," complains Dave Fisher, president of the High Desert Cattlemen's Association. "It's a bunch of bureaucratic malarkey, and the public is going to pay. In 15 years when hamburger hits $5 a pound, there'll be enough tortoises and people can eat them."

Burger prices are not the prime issue to Berry, 47. The daughter of a Defense Department scientist and a musician in the desert town of China Lake, Calif., Berry attended Stanford, then returned home to work for the Naval Weapons Center. "It wasn't exactly the kind of thing I like to do," she says wryly, and she soon headed for UCLA and Berkeley for advanced degrees in biology and zoology. She first formally met the Mojave tortoise in 1971, when the California Department of Transportation hired her to relocate several dozens of the reptiles living in the path of a future highway. "Unfortunately, relocations rarely work," Berry says. "These animals have territories. When you move them, they want to go home." She joined the Bureau of Land Management in 1974 and took up the tortoise cause full-time in 1983. That same year she married Ray Butler, 47, an ex-developer who shares her concern for wildlife.

Foes of the restrictions argue that ecosystems must have room for people too. "This is not simply a homebuilder's issue," says Terry Murphy, development specialist with the Southern Nevada Home Builders Association. "It affects the quality of life and public welfare of all residents." Berry, who has written an 850-page study of the desert tortoise, responds that only the new restrictions—which carry penalties of up to $100,000 and a year in prison—will leave the species any life at all. "The tortoise is a symbol of what's happening to deserts," she says. "Animals as well as people deserve a piece of the pie."

—Susan Reed, Tom Cunneff in Las Vegas