The Justice Department has settled with two major Alexandria waterfront landowners, including a subsidiary of The Washington Post Co., leaving only six small properties at odds with the federal government over who owns the city's valuable riverfront.

One out-of-court settlement involving owners of a 10.5 acre tract, just south of the Potomac Electric and Power Co. power plant, calls for 4.7 acres of the property, or 45 percent, to become public open space.

It stipulates that the tract's owners restore the old Alexandria canal lock and provide free space for a waterfront museum. It also permits a complex of four buildings, up to seven stories high, built on the hilly riverfront land.

The other settlement with Robinson Terminal Warehouse Corp., a newsprint handling and warehouse subsidiary, calls for the firm to turn over to the city at an unspecified time about two of its seven acres of prime Old Town waterfront land.

The firm is required to make immediate public park improvements at the ends of Oronoco, Duke and Wolfe streets, some on land that would be filled if the Army Corps of Engineers gives its approval. Most of the two acres would be relinquished under the settlement if the firm ceases to use the land for warehouse purposes.

The Northern Virginia Conservation Council has filed objections with District Court Judge John G. Penn and will attempt to intervene in the settlement near the power plant, claiming federal lawyers have been "giving away public land" in their negotiations.

Conservation Council President Ellen Pickering, a former member of the Alexandria City Council, this week called the Robinson settlement "a swindle in which some decorative improvements will be made at the ends of streets which the city already owns. . . It's a giveaway because the government probably owns all The Post land."

Alexandria Mayor Charles Beatley has called both settlements "reasonable compromises that recognize some grandfathered rights along the river but which restrict future use of the properties."

"We've been settling for what we feel is fair, considering what the U.S. claims and the defendants claim," said James Draude, the Justice attorney handling the government's decade-old suit over the waterfront. "In some cases we think we own all the land and in some cases maybe half of it."

The government claims title up to Potomac's 1791 high water mark, which was the city boundary when Virginia land designated as part of the nation's capital was retroceded to the state in the mid-1800s. Much of Alexandria's waterfront is filled land, and the federal government claims 30 to 40 acres of it.

Justice has not made public the exact amount of land it has claimed in any of the settled cases, said Draude. Its claims in the remaining six cases will be revealed if they go to trial. Draude expects the cases will be heard soon since few of the remaining property owners appear willing to settle.