California's golden grassland. WILDLIFE HAVEN SAVED

A NEWLY hatched golden eagle wobbles its downy gray head over the woven branches of its nest, high on a rocky outcrop. On a cave floor 30 feet below are bedrock mortars, hollowed pits where Chumash Indians once ground acorns into flour. The cave overlooks the heat-shimmering tans of the Carrizo Plain, where even the alkaline water of Soda Lake appears parched. Here, the Nature Conservancy is creating - 120 miles north of Los Angeles - one of the largest wildlife preserves in the United States. The environmental group paid $14 million for this high, wind-blown basin of salt flats, where sandhill cranes nest by the thousands each winter.

It's the Nature Conservancy's mission to find, purchase, and maintain areas like this, where rare and endangered species can be preserved. The 180,000 acres of desolate land that have been of little use to anyone else are an ecological treasure - a habitat that has nearly disappeared. This is the last substantial surviving remnant of the grasslands that once covered one-quarter of California.

The Carrizo acreage will join the world's largest private preserve system: 968 sanctuaries involving nearly 537,000 acres. Since 1951, the Nature Conservancy has saved more than 3 million acres, through nearly 5,000 projects, protecting more than 1,000 rare and endangered species. Much of the land is sold back to governmental agencies or other entities to be preserved. The conservancy's role is to move quickly when environmentally sensitive property comes on the market. With headquarters in Arlington, Va., and 310,000 dues-paying members, the nationwide staff of 800 has a $79 million revolving fund for this purpose.

``One of the reasons we're so successful in what we do is that we don't come off as rabid, screaming environmentalists,'' says Ken Wiley, Central Coast manager of the conservancy. ``We talk the language of planners and developers.''

The conservancy also works with partner organizations throughout Latin America, where it is developing a network of conservation data centers that keep track of endangered species. As a result of its land protection efforts in the Florida Keys and Hawaii, the organization was awarded a $3 million MacArthur Foundation grant last year. The group is known among environmentalists for its nonantagonistic, businesslike style.

``They're very good at what they set out to do, which is to preserve land from development,'' says Lawrie Mott, a senior scientist with the Natural Resources Defense Council. ``It's very different from the more confrontational efforts of advocacy groups like the NRDC or the Sierra Club.''

This was demonstrated in 1984 near Palm Springs, Calif. Real estate projects worth an estimated $19 billion had been tied up by concerns about the endangered Coachella Valley fringe-toed lizard. Rather than join litigation, the conservancy organized talks among all interested parties and then purchased 1,920 acres with $25 million, much of it raised from developers. That land became the core of a 13,000-acre tract. Real estate projects went ahead. And the fringe-toed lizard has a home.

For the purchase of the core 82,000 acres at the Carrizo Plain earlier this year, an unprecedented number of entities - 16 - cooperated in months of negotiations. They included oil companies like Tenneco and Shell, which own subsurface mineral rights; a real estate company, Oppenheimer Industries of Kansas City, which owned eight large ranches; and government agencies like the United States Bureau of Land Management, which owns much adjacent land.

The core acreage cost the conservancy $14.2 million, some of which was paid in a land swap of property near Fresno that had little biological value. Four million dollars in federal money contributed to the purchase. The conservancy will sell all but about 5,000 acres to the BLM and the California Department of Fish and Game's Wildlife Conservation Board as funds are available.

More rare and endangered vertebrates live on the Carrizo Plain than in any other area in California. They include the blunt-nosed lizard, the supremely photogenic San Joaquin kit fox, and the kangaroo rat, an endangered species common on the plain.

Tule elk and pronghorn antelope, which had been killed off on the plain, have already been reintroduced. In the future, condors may be released to forage on the 800,000 acres, including adjacent BLM and Forest Service lands, that will be protected in the heart of the California condor's historic feeding grounds.

The property will be co-managed by the Nature Conservancy and the BLM. Hiking will be allowed. Off-road vehicles will not. Grazing will be managed so as not to harm endangered species. Oil companies will still drill exploratory wells, but they have agreed to cooperate in preserving the habitat.

The Temblor Range, where the San Andreas fault is visible for miles as it cuts through a blanket of eroded ridges, separates the narrow Carrizo Plain from the broad San Joaquin Valley and its huge corporate farms. For years, the 2,000-foot range isolated the basin from irrigation and the booming changes in the rest of the West.

As it is, dry-land farming of barley on the plain is marginal. Oil drilling thus far has been unsuccessful. Electricity comes from generators. Communication is by radio phone. The nearest gas pump is 45 miles away, over the La Panza Range.

Life has been pretty slow for the area's 200 inhabitants, says Richard Burgett, owner of the California Valley Restaurant, the only place to buy a cup of coffee on the 400-square-mile plain.

``It's got to be an emergency,'' Mr. Burgett says, ``to keep people from taking a nap.''

``There's some humor for us in protecting the kangaroo rat,'' he says. ``When it comes in your house, it's not an endangered species. It's a rat.''

The Nature Conservancy's plans include seeding 40,000 acres with saltbush scrub, a native plant community that supports several endangered species. Ranchers on the plain have been fighting saltbush for generations.

``We may actually contract with these guys to farm the saltbush for us,'' Mr. Wiley says. ``They go, `OK. That's what the boys from San Francisco want, the guys with the bird books and binoculars.' I think we all enjoy the irony.''