IT IS HARD to believe that 47 years of U.S. Army duty could enhance the beauty of something. But that appears to be the fate of a Potomac River peninsula known informally as the Woodbridge Refuge.

In 1949 the Army bought a cattle farm -- about 600 acres at the confluence of the Potomac and Occoquan rivers -- and turned it into a transmitting station. Two decadeslater the Army took down the radio antennas and converted the site into a test range for electromagnetic experiments. Now, having wrapped up that research, the Army is ready to give the land to the U.S. Fish & Wildlife Service, which will turn it into a haven for nature lovers.

To understand how the place has changed, listen first to Peter Dawson, who spent his summers there before the Army rolled in and fenced it off. "It was a wide-open working farm with not that much cover for wildlife, except around the periphery," says Dawson, a retired pilot whose family owned the farm from 1909 to 1949. "I never saw a deer down there. We used to go turkey hunting every fall, and I never saw a turkey."

Now listen to botanist Nicky Staunton and birder Jim Waggener as they tour the peninsula in Staunton's white Ford Explorer. It's a warm October morning, and they've just glimpsed a large bird hovering a few feet over a meadow.

"It's harrier behavior," Staunton says, lifting her binoculars.

"He's got a white chevron across his rump on the top," says Waggener, who then confirms the ID: northern harrier. "This one's brown. I think this is a female. The males are a beautiful pearl gray."

After the harrier disappears into tall grass, Waggener says, "This bird would not be here if we did not have a good, strong small-mammal population" -- mice, voles and shrews.

"And they wouldn't be here if we didn't have this overgrowth of gama grass," says Staunton. "This plant has grain on its stem, and in the winter it clumps down and makes great habitat for little rodents."

As the Explorer crosses a culvert near the property's center, Staunton motions to swampy areas on the left and right. "Down here is a favorite spot for us botanically," she says.

"It's a terrific place for birds," Waggener adds.

"We found frog-bit here, which is a heart-shaped leaf with a spongy underpart to it," Staunton says. "And over here in this ditch we usually see frogs and snakes and forget-me-nots."

"The king rail nested here this summer," Waggener volunteers. "And woodcock have nested up here on the other side of the road."

Officially, the property is still the Woodbridge Research Facility, run by the Army Research Laboratory. After Fish & Wildlife begins managing it (which may occur this month), volunteers will start fixing its bumpy gravel roads and building boardwalks, trails and viewing platforms.

A year from now, the place should be open to the public. Meantime, you can see it by joining field trips run by various birding clubs (listed below).

By special arrangement, Waggener has been scoping out birdlife on the peninsula since 1990, and Staunton has been studying plants there since 1993. They've basically served as scouts for the naturalist community, and the news they bring is tantalizing. "Of the 243 {bird} species that are documented for Prince William County, 214 have so far been found right here in one square mile," says Waggener. As for plants, Staunton reports that 540 species have been found growing in 20 different habitats.

Twenty habitats in a square mile! If you're a nature watcher, this level of variety means you can see a lot of good stuff in a single, easy hike.

Naturalists who've visited recently are especially abuzz over the peninsula's generous expanse of meadows. For nearly half a century, the Army routinely mowed these open areas for its own security and convenience. After Army researchers vacated the premises, leaving behind only a security detail, the mowing stopped. The fields grew wild, creating a rodent paradise which, in turn, attracted large numbers of raptors and songbirds.

"The open meadows are extremely important to migratory songbirds," says Dennis Shiflett, a Virginia Wildlife Federation official who lobbied for the land transfer to Fish & Wildlife. Because the refuge lies across Occoquan Bay from Mason Neck National Wildlife Refuge, Shiflett says, it provides perfect foraging habitat for eagles and other raptors that nest in Mason Neck's hardwood trees.

Craig Koppie, a Fish & Wildlife biologist who has studied birds in the Mason Neck area, says the waters off the Woodbridge Refuge attract huge numbers of wood ducks -- migrants as well as nesting ducks. Flocks are easily visible from a few points on the shore.

"A lot of folks down there don't even know {the refuge} exists," Koppie says. "The Army has had it closed off for so many years, people think the end of Dawson Beach Road is just locked up. One day soon, it'll be open to the public and will be a great place for birders."

Before the refuge can be counted among the region's finest natural areas, its managers must solve a couple of problems. One is soil contamination at a few scattered sites. The Army apparently spilled some PCBs when disposing of old electrical equipment. Cleanup has been underway for a decade and should be completed by next summer, according to Todd Waltemyer, the Army's site manager.

Frederick Milton, who'll manage the refuge for Fish & Wildlife, says the polluted spots will be kept off-limits to hikers until the cleanup is complete. He says that visitors who avoid the posted areas needn't worry about possible contact with PCBs.

Cynthia Pruett, a birder who is co-chair of a group that has been monitoring the cleanup, agrees with Milton. The refuge "is really not a high-risk site at all," says Pruett, president of the Fairfax Audubon Society. So people should "absolutely not" have any trepidation about walking around there.

The second problem facing refuge managers is how to pay for such things as trails, boardwalks, a visitors center, descriptive literature and upkeep of the property. The solution seems to lie at the center of the site, where the Army constructed a small campus for its workers. These four buildings, now empty, will make serviceable classrooms, labs and offices for schools that aim to use the refuge as a teaching facility. George Mason University, Northern Virginia Community College and the Prince William County public school system are among the groups that plan to lease space from Fish & Wildlife.

With educators, birders and others hoping to enjoy the property, a fair sharing arrangement will have to be devised. Milton and Waggener are among the people working on this task.

Waggener, a retired Air Force colonel who lives near the refuge, heads a group called the Prince William Natural Resources Council. He's generally described as the guy who led the campaign to get the site incorporated into the Mason Neck Wildlife Refuge. (For a time, the Library of Congress eyed the property as a potential warehouse site.)

As Waggener continues his tour with Staunton, he sees a red-shouldered hawk, a flock of bobwhites, a painted turtle, an immature eagle, a brown thrasher . . . and then, a pickup truck.

Poking his head out the window, Waggener greets Army site manager Waltemyer as the two vehicles squeeze past each other.

"Have you seen the turkey?" Waggener asks.

"No," says Waltemyer.

"Frederick {Milton} saw it yesterday, over on the Belmont fence line again." "I'm anxious to see it," says Waltemyer. "I've got my camera with me."

As the Army prepares to vacate, its personnel are roving the site armed with cameras. That should tell you a lot about this place. THE WOODBRIDGE REFUGE -- At the south end of Dawson Beach Road, just off Route 1 in Woodbridge. It is not yet open to the public, but you can see it on free or inexpensive outings organized by the Audubon Naturalist Society (301/652-9188, Ext. 3006), the Northern Virginia Bird Club (703/560-4950) and the Fairfax Audubon Society (703/256-6895). You can also arrange to come with your own group by calling the Friends of the Woodbridge Refuge (703/497-0506). Field Trips-related e-mail should go to: FREE PROGRAMS BIRD WALKS -- Led by veteran birders and sponsored by Wild Bird Centers of America, are held frequently throughout the year. For information, contact the shop near you. In the District, 202/244-9453. In Maryland: Annapolis, 410/573-0345; Bowie, 301/805-4858; Cabin John, 301/229-3141; Columbia, 301/596-2990; Gaithersburg, 301/330-9453; Rockville, 301/468-7333; Silver Spring, 301/681-4077; Waldorf, 301/843-2994. In Virginia: Alexandria, 703/370-5544; Burke, 703/323-7898; Centreville, 703/818-9453; Woodbridge, 703/878-6688. MEET RAPTORS -- On Saturday at 2 p.m., take a close look at hawks and other birds of prey living at Potomac Overlook Regional Park Nature Center, and learn about raptors common to this area. The park is located at the end of Marcey Road, off Military Road in North Arlington. Reservations required. Call 703/528-5406. WOLVES UP CLOSE -- On Nov. 19 at 8 p.m., see live gray wolves on display as part of Mission Wolf's nationwide tour to raise awareness about wild wolves. Sponsored by the Fairfax Audubon Society, the program will be held at the National Wildlife Federation, 8925 Leesburg Pike, Vienna. For information, call 703/256-6895. Next week in this space: In Motion consults experts on what exercise equipment they recommend for several different budgets. CAPTION: Pickerelweed and hibiscus bloom in a Woodbridge Refuge tidal marsh, left. On higher ground, fields of gama grass shelter rodents and make good hunting grounds for raptors as well as this fox, above.