More than 400 refuges on 90 million acres form the National Wildlife Refuge System, created in 1903 to protect the egrets and herons of tiny Pelican Island in Florida. The refuges are administered by the U.S. Fish and Wildlife Service.

Most refuges provide a habitat primarily for migratory birds, but several, like the National Elk Refuge, feature other large wildlife in substantial numbers. But you may need persistence and binoculars to spot some of the shyer animals.

Among the refuges:

* National Bison Range, Moiese, Mont.: From 325 to 400 bison roam 19,000 acres of hilly grasslands in the Flathead Valley north of Missoula. Red Sleep Mountain Drive is a 19-mile self-guided tour from the visitor's center.

* Fort Niobrara National Wildlife Refuge, Valentine, Neb.: Herds of purebred Texas longhorn cattle (275), bison (225) and elk (40) and a 30-acre prairie-dog town occupy 19,000 acres along the Niobrara River in north central Nebraska. Lots of calves in June. Self-guided drive through the pastures.

* Desert National Wildlife Range, Las Vegas, Nev.: About 1,500 to 1,800 desert bighorn sheep keep to the high mountain ranges just north of Las Vegas, and you have to look hard to see any on the refuge's 1.5 million acres. Best spots are summer water holes, reached by rugged wilderness backpacking trails.

* Hart Mountain National Antelope Refuge, Plush, Ore.: The sagebrush slopes of Hart Mountain, an 8,000-foot volcanic ridge in south-central Oregon, is the summer range of 800 pronghorn antelope. Soak in the rock basin hot spring at the visitor's center.

* National Key Deer Refuge, Big Pine Key, Fla.: A cluster of keys, most accessible only by boat, are home to 250 to 300 of the small white-tail deer. A self-guided driving tour on No Name Key, adjacent to Big Pine.

* Kenai National Wildlife Refuge, Soldotna, Alaska: Once it was named the National Moose Range, and moose remain the outstanding wildlife species. Camping and backpacking in a 2-million-acre wilderness of lakes, spruce and birch forests and mountain glaciers in southern Alaska.

* Crystal River National Wildlife Refuge, Crystal River, Fla.: The endangered manatee or sea cow, a huge (up to 1,500 pounds) but harmless aquatic mammal, winters in the salt-water bays and estuaries on the Florida Gulf Coast north of St. Petersburg. Glass-bottom boat tour, or you can snorkel among them (about 140), but don't touch.