Negotiations aimed at ending a bitter dispute between Alexandria and the federal government over ownership of the city's waterfront were abruptly canceled yesterday when a former Alexandria official barged into a closed meeting and refused to leave.

Mayor Charles E. Beatley Jr., city manager Douglas Harman and officials of three federal agencies watched with red faces and open mouths as former council member Ellen Pickering and environmentalist Marian Agnew sat down in Harman's office.

"I am concerned about backroom deals being made over the waterfront," announced Pickering, a political independent who was defeated for reelection in last June's election.

"I apologize for the actions of these . . . pests," Vice Mayor Robert L. Calhoun snapped to the federal officials.

"We are trying to lay the groundwork here for an orderly resolution of the dispute," Beatley said, pleading with Pickering to leave. "We will not be making any decisions," the mayor said. "There are legal matters to be discussed here."

"I am sorry if other people don't know their rights," retorted Pickering, whose stated position during her three years on the council was that the city waterfront should be turned into a public park. "I will not leave."

The meeting had to be arranged to discuss a possible solution to the Interior Department's 1973 lawsuit over ownership of the Potomac River waterfront. Largely at the request of various environmental groups, the department sued the city in federal court hoping to block city plans for high-rise buildings that the department claimed would despoil the Washington skyline.

Since the suit was filed, Alexandria has changed its zoning ordinances, prohibiting high-rises along the rivers. It also has issued a comprehensive plan for the riverfront that in many respects parallels a federal proposal issued last month.

Similarities between the two plans led city officials to believe a resolution of the dispute, which has stalled waterfront development in the city, could be at hand.

City Attorney Cyril D. Calley said yesterday's meeting could be closed under Virginia's open meeting law since only two elected officials -- Beatley and Calhoun -- were present.

But Beatley announced that it would be "unfair" to other city residents if only Pickering and Agnew were permitted to attend the negotiation. "Other people have been told all week long that this will be a closed meeting," he said, leaning wearily against Harman's desk. "We will schedule a public hearing on this in the future."

With that, the top-ranking officials from the Interior Department, the Department of Justice, and the attorney general's office picked up their charts and left.

"Oh, I guess we'll be back," Jack Fish, regional director of the Interior Department said, alternately laughing and scowling.

But while Beatley was optimistic about future discussions, he acknowledged that the meeting yesterday had been arranged only after numerous earlier meetings had been canceled by the federal officials.

"It's clear that Mrs. Pickering's aim is for the federal officials to own and operate the land," said Harman. "This is a shame." He labeled as "absurd" Pickering's charges about "backroom deals."