TUCSON, Ariz. -- Thorny mesquite and prickly pears stretch for miles off Old Spanish Trail. Roadrunners zip through the underbrush.

		GILBERT W. ARIAS / P-I
	Housing is developed in high density in Pima County's Oro Valley, north of Tucson, Ariz. The county's proposed 610,000-acre habitat conservation plan was pushed by environmentalists and is based on hard science.

Turn off the highway southeast of here, past the warning CATTLE MAY BE PRESENT -- BE ALERT and suddenly a development pops into view like a stucco-plastered mirage. Colorful flags and balloons beckon homebuyers.

The scene is repeated over and over, as developers race to accommodate the region's rapid growth -- which isn't expected to slow anytime soon.

"It's painful to watch it get bulldozed up and become air-conditioned subdivisions," said Linwood Smith, a consulting biologist and longtime resident.

Now home to 930,000 residents, Pima County -- Tucson is the county seat -- is expected to accommodate 1.3 million people in the next two decades. But a host of animals are fighting for their toehold in the desert, too.

There's the lesser long-nosed bat, Gila topminnow, Chiricahua leopard frog and other crafty creatures that have evolved to withstand the desert climate.

Local government officials, environmentalists and scientists are trying to help. They are nearing completion of a habitat conservation plan that protects swaths of desert most crucial to the survival of these vanishing species, corralling clusters of development into less-fragile territories.

		GILBERT W. ARIAS / P-I
	Saguaro cactuses like this one near the Tortolita Mountains north of Tucson are home to the endangered cactus ferruginous pygmy owl.

Nearly a decade ago, the nation's first large-scale urban habitat plan was approved in central Texas. The Pima County plan aims to improve on that, and the model that is emerging has captured national attention.

"Pima County is a really important model because it is a comprehensive, general land-use, habitat protection plan," said Bruce Babbitt, the former head of the Interior Department who championed the conservation program. "It goes a long ways beyond the specific requirements."

The 610,000-acre plan aims to save the area's Sonoran Desert ecosystem -- not just a few endangered species. The effort turned the national program on its head -- spawned not by the developers, timber companies and landowners who usually push for the plans, but by environmentalists.

It is built on rock-solid science, drawing on the expertise of some 400 researchers -- the broadest scientific consensus in the 23-year history of the federal habitat program. The process itself has also been unusually open, with scores of public meetings.

"We wanted it to be different," said Carolyn Campbell of the Coalition for Sonoran Desert Protection, a Tucson-based environmental group. "We wanted to be in the forefront."

		GILBERT W. ARIAS / P-I
	A roadrunner keeps his eyes on visitors to the Sonoran desert.

The plan, which has been in the works for seven years, is expected to be submitted later this year to the U.S. Fish and Wildlife Service. Some key details -- the total area that will be set aside in preserves, the plan's duration and the number of species protected -- remain uncertain.

About 250 studies of the desert ecosystem helped shape the plan's conservation strategy. Scientists, who were recruited early on, have been uncharacteristically free from pressure to alter the plan to meet political and development demands, they say.

Whether or not the plan is approved, "we didn't care," said Bill Shaw, a wildlife professor at the University of Arizona who led the effort. "We're going to plan for saving biological diversity and see how it goes."

That has involved a detailed examination of 55 desert plants and animals to determine where they live, what they need to survive and threats to their existence.

The creatures here, many of them prickly and thick-skinned, remain fragile. They form complex relationships with one another to ensure survival in the arid lands. Scruffy ironwood, which can live 800 years, serve as "nurse trees" to young cactuses, providing shade in the summer and warmth in the winter. Tiny owls seek refuge in abandoned woodpecker holes bored into saguaro cactus. Everything is linked by a need for water.

The result is a proposal to restrict development in areas along streams -- leaving 95 percent of the land undisturbed. In less sensitive spots, up to 75 percent of the land would be left alone.

The long-term strategy has won unlikely supporters, including some ranchers and real estate agents.

Mac Donaldson is a second-generation cattleman on a ranch southeast of Tucson in the surprisingly lush, oak-dotted Chihuahua grasslands. "We are in a desert, and you can't populate it to death," he said. "Most of the ranchers look at open space and protection of the habitat as positive."

Developers remain skeptical. They have weighed the cost of land-use restrictions against protection from lawsuits for harming endangered species. The result is a resigned acceptance.

"The pros and cons are equally balanced," said Ed Taczanowsky, president of the Southern Arizona Home Builders Association. "I'm not going to say anything bad about it."

There's a sense of urgency to get the plan in motion. One of the plan's most important species, the endangered cactus ferruginous pygmy owl, has nearly been run out of the state. Only 31 of the owls -- a messenger of the dead, according to Indian lore -- are known to remain. They're all in Pima County.

Crucial money issues must be resolved. The county passed a $174 million bond last year to buy land for preserves, but a long-term source of funding for managing those lands hasn't been set.

Tucson, the area's largest city, opted not to join the county habitat plan and doesn't expect to finalize its own for another three years. In the meantime, construction marches on and valuable land is lost, environmentalists say.

Still, there's reason for optimism. Some 72,000 acres have been protected, and conservation-oriented zoning strategies have already been adopted by the county.

"Even before we apply for the permit, we're already 10 years ahead," boasted Maeveen Behan, a county administrator and architect of the conservation plan.

Environmentalists are heartened most by the county's expressed intent to promote recovery of endangered species -- going beyond the usual goal of maintaining the status quo.

The cheering section extends to Bill Arnold, a Realtor who has lived in the area for decades.

"I hope that my grandkids are going to say, 'Grandpa had a hand in this and this is really cool,' " he said. "There's a legacy here for the community, and I'm proud to be a part of it."

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