There are only 1,200 known pairs of nesting bald eagles in the lower 48 United States. Some serious lovers of the outdoors have spent years staring at the skies and treetops looking for a sign of our endangered national symbol without seeing their first eagle.

So when Jim Williams, who runs the Mason Neck Wildlife Refuge near Lorton, called to say mature eagles were out for the watching at nearby Pohick Bay Regional Park last week, we hurried for the car.

Williams met us at his office behind a pizza shack on Rte. 1 in Northern Virginia. We piled into his car and in 15 minutes we were pulling alongside the boarded-up refreshment stand at the park.

"They should be right over there," said Williams' assistant, Steve Wunderley, waving at a point of land jutting out into the bay 300 yards away "Holy catfish," said Williams, "there he is."

He pointed to a clump of trees at the tip of the point, and from one of the tallest hardwoods a big, dark shape lifted off and began a slow, lazy spiral skyward.

"It's an eagle, for sure," said Wunderley, who had unsheathed his field glasses. "And look, there's another one perched on the tree."

Soon, the second bird lifted off, but it went the other way, over a rise, and disappeared.

The first eagle reached cruising altitude and began a series of long, looping circles as it moved closer to us. With Williams' powerful glasses, I could first pick up the sweep of the broad wings, and when it was almost above us, 200 yards high, I could clearly make out the bright white patches of the head and tail and the squat powerful neck. An eagle, no question.

Williams expected the eagle to hang around in the bay, fishing for its supper, but when it spotted us below it spooked and flapped away into the marsh.

"He'll be back," said Williams, who had watched eagles from this vantage point before.

While we waited, he explained about Mason Neck, the 1,600-acre refuge he runs for the Interior Department. It's closed to the public until April 1 because its principal mission is to provide nesting habitats for bald eagles.

The eagles establish nests this time of year, and even the best-intentioned birdwatchers could harass a pair off the nest. But the pair we watched were on property of the regional park, which is open to the public all year, and there was little harm to be done by watching from the snack shop, Williams said.

Mason Neck has had a pair of eagles nesting for several years, but in the last year there have been some dramatic advances.

For one thing, there is a new female nesting there, and eggs taken from her nest for testing have proven to be untainted by contaminants. Her predecessors' eggs were sterile. Williams and Wunderley have high hopes that there will be a baby eagle at Mason Neck this spring.

In addition, eagle numbers are up. The men made their winter count last weekend and came up with seven eagles, five more than they've found in any recent year.

Mason Neck is about as far up the Potomac as eagles will nest. They seem to do a U-turn when they get to the urban sprawl of Washington and Alexandria.

Until last year, their nesting here was fruitless. The female of the Mason Neck pair apparently was so contaminated by PCBs -- chemical pollutants -- that her eggs would not hatch.

Last year, that female disappeared and a younger, uncontaminated female took her place.

It is an advance to be cheered because eagles are terribly scarce in many parts of the Northeast. Dr. Stanley Weimeyer, eagle specialist at the Interior Department's Patuxent Wildlife Research Center, said New York State is down to one nesting pair, as are North Carolina and New Jersey. The lower New England states once had some breeding pairs but now have none at all.

The key problem has been contaminants in water and the fish that eagles eat. DDT destroyed the birds' eggs, as did the insecticide dieldrin. Both are banned now.PCBs also are harmful and they are coming under increasing government control, Weimeyer said.

The result is that eagles are beginning to show signs of reproductive recovery. Weimeyer said the normal reproduction rate is one nestling a year per active pair. In the early 1960s, that fell to one-fifth of a young per pair. Now the rate is back almost to normal in Maryland and about half of normal in Virginia, where trouble persists around the York and James rivers.

Weimeyer is pleased, but he remains concerned about Mason Neck, where he says "something still isn't right."

But it's better than it was. Late in the day, the eagle we had watched when we arrived returned, although this time it kept its distance.

As darkness gathered, we packed up and headed out.As we neared the gate, Wunderley grabbed his glasses. "It's another one -- look over there," he said.

Nestled in the water was a large bird, but the wrong kind. "Looks like a heron to me," Williams said. "Look, it's got a fish."

At that moment, another great bird soared into view and perched on a tree directly over the first bird's head.

"Now that is an eagle," said Williams, and we laughed as we watched the heron gulp down the fish. "He knows that eagle wants to take it away," Wunderley said.

We spooked that eagle, too, but as we crept near, still another one hove into view, making four for the day. This one was immature, with no white markings. The two great birds joined up, flew across the bay and lighted in a pair of trees, where they sat contentedly while we watched them through the glasses.

Directions: There are signs for the Pohick Bay Regional Park at the Lorton exit off I-95. Follow the signs into the park, then take the road to the water and the refreshment stand. The eagles should be off to the right, and identifiable by their white heads and tails. Bring field glasses and a field guide.

The birds often fish in the bay, according to Williams, and if you are lucky you'll see them scoop up a fish or even nail a duck or a muskrat.

If you are extraordinarily lucky, you'll see what Wunderley witnessed over the marsh last year -- the mating ritual of a mature pair, which occurs this time of year.

The eagles swooped and dove at each other, Wunderley said, and then both flew straight up until they were only specks in the sky. At some high point they clasped talons, folded wings and came plummeting to earth like stones, breaking up 200 feet above the marsh and swooping off to do it again.

Wunderley watched it three times, his heart in his mouth. Weimeyer said it's standard courting fare, but only a preliminary. "They actually mate later, on a perch."