Water is not what comes to mind in this sun-bleached landscape of crumpled mountains and creosote-coated basins. But that is what Las Vegas thinks of when it glances across its northern border at this sprawling bighorn sheep refuge, the largest federal wildlife sanctuary in the lower 48 states.

The city of water-themed casinos and ever-expanding subdivisions is looking here to begin a massive pumping project that would reach deep into rural Nevada to tap an ancient aquifer running from western Utah to Death Valley National Park in eastern California.

In Nevada's scrappy outback, the plans have prompted comparisons to Owens Valley, Los Angeles's infamous eastern Sierra water grab of a century ago.

Federal hydrologists worry that the first round of pumping, which if approved by the state engineer could be underway by 2007, could starve springs on public lands. They are concerned not just for this place but for several other national wildlife refuges in southern Nevada that provide havens for endangered species found nowhere else in the world.

In Death Valley and surrounding Inyo County, Calif., officials believe the pumping could jeopardize water supplies. "There's no doubt the aquifer will be drawn down. It's a question of magnitude and where it will occur," Death Valley hydrologist Terry Fisk said. "In our view, the withdrawal of water . . . could potentially harm our senior water rights."

The Southern Nevada Water Authority, the agency that manages the region's water supplies, says the pumping will have minimal, if any, effect. If they are wrong, authority officials say, they will turn off the offending pumps. "We've made a commitment if one of our wells causes environmental degradation, we'll shut it off," said Pat Mulroy, the agency's general manager.

The groundwater development is just one of several fronts her agency is pursuing as it hunts for more water for fast-growing Las Vegas, which gets most of its municipal supply from the fully claimed Colorado River, now in the grip of what some experts say might be the worst drought in 500 years.

The authority has obtained rights to divert water from the Virgin River northeast of Las Vegas, has expressed interest in buying irrigation water from other states and has lobbied the federal government for a bigger share of the Colorado.

"Something has to give. Southern Nevada is the economic engine in the state of Nevada," Mulroy said.

In the past year, thanks to drought measures, regional water demand dropped, reversing a more than decade-long trend during which water use jumped from about 300,000 acre-feet to more than 500,000 acre-feet. (An acre-foot is the amount of water that would cover 1 acre to a depth of 1 foot. One acre-foot is enough to supply two average homes for a year.)

But every month, the Las Vegas metropolitan area continues to grow by another 3,000 to 4,000 people. The groundwater system that the authority is proposing to meet new demand would take a decade to fully develop and could eventually deliver enough water to supply more than 300,000 homes.

The Nevada congressional delegation introduced a bill in June that would grant the water authority pipeline rights of way across federal land.

The authority would like to start here, pumping enough water from beneath the 1.6-million-acre desert range and nearby basins to annually fill a 3-mile-high football stadium.

Established in 1936 to protect desert bighorn sheep, the refuge has the stark, unforgiving contours of a place where summer temperatures reach 117 degrees and annual rainfall averages 4 inches on the valley floors. More than three-fourths of the refuge is pristine enough to have been recommended for inclusion in the federal wilderness system.

"We have some very serious concerns about the effect of withdrawing that much water," said Dick Birger, a veteran U.S. Fish and Wildlife Service manager who oversees the desert refuge and three other much smaller refuges nearby. "Any creature that can live in the Mojave [Desert] is already on the ragged edge. There's no fat in survival in the Mojave."

At the other wildlife sanctuaries -- Moapa Valley, Ash Meadows and Pahranagat -- warm springs bubbling from the earth provide a home for remnant fish and aquatic life left over from prehistoric times, when Nevada was a place of lakes and plentiful water.

"The species we're talking about occur only here," said Cynthia Martinez, an assistant field supervisor for the Fish and Wildlife Service in southern Nevada. "When the water's gone, they're gone. There's no place else to put them."

Refuge officials think spring flows at Moapa are already dropping because of nearby groundwater pumping started in the late 1990s by a local water district.

Water managers say the drought might have more to do with the Moapa spring decline than any current pumping, a disagreement that presages the quandary officials could face if Las Vegas withdraws large amounts of groundwater and springs start drying up.

"Who decides who's to blame? Who decides who's having the impact?" wondered Tim Mayer, a hydrologic engineer for the Fish and Wildlife Service's western region. "It's very hard to agree on these things."

The Southern Nevada Water Authority says the worries of federal agencies are not justified. "I don't disagree that any time you change scenarios there may be a minimal impact. That is the key: minimizing," said Kenneth Albright, resources director at the authority. "Our proposal is to develop a series of resources that we can manage. We don't plan on pumping or diverting from any resources 365 days a year," he said.

But Death Valley officials are concerned about springs that supply eastern portions of the park as well as Devil's Hole, a tiny holding just across the Nevada border. The water-filled underground cavern was the site of a 1970s legal battle that was resolved when the Supreme Court halted groundwater pumping by a nearby ranch that was threatening to wipe out its resident endangered fish.

And a few miles to the west, officials in Inyo County are nervously following the pumping plans.

"We are cautioning Nevada to be careful," said Greg James, special legal counsel to the county, which has had protracted battles with Los Angeles over Owens Valley water exports. "Once the water is going to the city, it's very hard to get it back. And it's hard to restore the environment that's been affected."

The Las Vegas pumping would draw at least in part from a vast underground aquifer known as the carbonate aquifer, named after the type of rock it occupies. It extends from beneath western Utah through eastern and southern Nevada to Death Valley in eastern California. Several miles thick, it holds an enormous amount of water, much of it stored for thousands of years after falling as rain or snow during much wetter eras.

"It's a huge aquifer system," acknowledged Dan McGlothlin, supervisory hydrologist for the National Park Service's water rights branch. "But the recharge in relation to the storage is so small, and if you look at it as a bathtub with water spilling over -- if you draw water down so you no longer have flow over the top of the bathtub, you have essentially dried up the springs."

Environmentalists complain that there is no room for mistakes in places such as Death Valley and the desert refuge.

"Nobody is denying Nevada has a need for more water," said Don Barry, executive vice president of the Wilderness Society and a former Interior Department official who oversaw the Park Service and the Fish and Wildlife Service during President Bill Clinton's second term. "I just think a national wildlife refuge should be the last place you go to get it."

Warm springs bubbling from the earth provide a home for remnant fish and aquatic life left over from prehistoric times. Dick Birger and Amy Sprunger-Allworth of the U.S. Fish and Wildlife Service patrol the Desert National Wildlife Refuge in Nevada.