One of metropolitan Washington's more unusual properties, a 45-year-old, man-made island on the Prince William-Fairfax county line in Occoquan Bay, is for sale for an asking price of $49,500.

It comes complete with one medium-sized tree, two small ones, a good stand of grass and two duck blinds on its 0.174 acres.

Its owner, William E. Howard, 61, of Gunston, describes it as a bargain, "It would cost $200,000 to build an island like this one now. And anyway, the government wouldn't let you do it," he said.

An Army Corps of Engineers spokesman confirmed that there will not be another island built like this one was, right in the middle of Occoquan Bay.

But so far, Howard has had no takers and the sort of price he may finally get is hard to estimate. Prince William appraises the island at $500 for tax purposes.

Vernon Hicks Jr., who leased the island for duck hunting for 10 years until open-heart surgery slowed him down a year ago, said, "It's an ideal spot for duck hunting, but I don't know what else you could do with it."

The hunting is not what it used to be, in the days before pollution and development killed the marsh grasses that ducks feed on and game wardens put a stop to baiting, but it is still good, Hicks said.

"You use decoys and a good caller helps," he said. "It's particularly good when the creeks along the shore freeze up a little. An outstanding place for canvasbacks."

The island exists because of ducks. The now extinct but once eexclusive Belmont Bay Gunning Club was about one mile away on the Fairfax shore and the members decided to build an island in 1932.

One member was the owner of the Smoot Sand and Gravel Corp. in Washington and he sent down a barge with concrete retaining walls built up from its sides. The barge was sunk, filled with dirt so that plants would grow and then surrounded with rock. It was an almost instant island.

Howard's father and later Howard himself worked as guides for the club during hunting season and as commercial fishermen the rest of the year, Howard said. The club faded away as bag limits shrank and ducks became scarcer, and about 1940 the island and club site were bought by the Smoot family, Howard said. Howard bought the island from them in 1973 for what he described as "a real good price."

Now, he said, he can no longer stand the cold enough to hunt ducks and would like to see a group of people get together and buy this island.

If Howard is able to sell his island, he will be left with one other strange relic of duck killing days - a "big gun."

The weapon is about 10 feet long, weighs about 175 pounds and has a two-inch barrel at the little end, Howard said. The gun would be loaded with a pound of shot, placed lengthwise in a small skiff and fired into a feeding flock after a careful approach. A single blast might bag 100 ducks, which could be sold for $2 each, Howard said.

The big gun was last fired in the 1930s, Howard said, years after it had been outlawed. It had to be hidden in the woods in order to evade the authorities but his father was never caught using it, Howard said.