JOHN JAMES AUDUBON, the 19th-century artist most famous for his dramatic and meticulous illustrations of North American birds, had to get his specimens the hard way--with his own gunpowder. Audubon spent as much time in the underbrush as in the studio, stalking his "models" and killing them with as little muss as possible so that he might have intact subjects for his drawings and watercolors.

Fortunately, nature artists in the Washington area have a much less bloody and time-consuming option: the National Museum of Natural History's Naturalist Center in Leesburg. The study collection housed there, stacked to the ceiling in a large warehouse-style space, contains nearly 30,000 animals, fossils, mineral objects and archaeological artifacts. All of the items are available year-round to researchers and to anyone with the itch to paint, draw, photograph or sculpt a piece of the natural world.

The collection will be an especially enticing destination Saturday, when the Naturalist Center holds its fourth and final Draw-In of 1999. These Draw-Ins, which are free, have become one of the Center's most popular events, attracting hundreds of artists each year. Some find new and exotic animals to depict, while others opt for old and familiar subjects.

The possibilities include posed and mounted animals, "skins" (study specimens with their insides removed), bones of astonishing variety and a wall full of "wet specimens," those things floating in jars that made high-school biology a little queasy for the rest of us. Artists make their own choices, from the smallest insects in need of magnification to the room's giant polar bear, 10 feet high on its hind legs.

Take your pick: The fruit bat, wings spread and teeth bared? The hefty, gnarled foot of an elephant skeleton? A very large and noble-eyed gray wolf? Or that 375 million-year-old tree stump spread ominously in one corner? Whatever an artist's pleasure, Naturalist Center staff and volunteers will help to find the specimen and create a comfortable work space. And not to worry if that four-foot-high tiger seems a little too genuine.

"A lot of people ask if our animals are real," explains Sally Rubal, teacher-naturalist at the Center. "We tell them, 'Yes, they are, but that doesn't mean any of them are alive.' "

Though the Naturalist Center and its collection are always open to school groups, scholars and artists, the Draw-Ins provide a unique set of additional resources. Docents with particular specialties are present to identify and research unusual specimens, and several professional scientific and commercial illustrators also participate, giving demonstrations and offering tips and techniques to novices and experienced amateurs alike.

"It's the great feeling of being here with all these other artists," says Helene Lisy, assistant manager of the Naturalist Center and organizer of Saturday's Draw-In. "We get teenagers and people in their eighties and nineties. These are people who want to stretch their minds."

Visitors must be at least 10 years of age and must bring their own materials. Past Draw-Ins have attracted sketch artists, oil painters, photographers, watercolorists, sculptors, digital illustrators and even, once, a young man toting an Etch-A-Sketch.

"He spent all his time drawing a murex shell, and it was perfect," Lisy says. "It was a shame when he had to erase it."

DRAW-IN -- Saturday from 11 to 4, at the National Museum of Natural History Naturalist Center, 741 Miller Dr., Suite G2, Leesburg. (Directions: Take Route 7 west to Leesburg; exit onto bypass, Route 7 west/Route 15 south. Turn left at Sycolin Road, and right at Miller Drive. The Naturalist Center is the first building on the left.) 703/779-9712 or 800/729-7725. Open 10:30 to 4, Tuesday through Saturday. Free admission.