For nearly two decades, Katie Lang has made a mockery of the cliche' "you can't fight city hall." But her long stretch of defiance may have finally ended.

Since 1974 Lang has been tilting with Alexandria officials over ownership of a prime piece of waterfront property where she has operated first a marina, then a parking lot for more than 27 years. The federal government also weighed in with its own claim to the site, on South Union Street near the heart of Old Town.

Late Sunday, in the wake of a federal judge's decision erasing Lang from the three-part equation, city workers set up concrete barriers at the two entrances to the parking lot. They also erected steel gates at the two-acre site, known as the Old Town Yacht Basin, and padlocked them.

Clearly, Alexandria officials were taking no chances with Lang, a silver-haired, blue-eyed woman believed to be nearing octogenarian status.

A federal judge recently ruled that the riverfront property, valued at $8.8 million, belongs either to the city or the federal government -- both of which would like to turn it over to the public, probably as a marina -- in effect, dismissing the claim of Lang, whom some city officials have dubbed the "ultimate squatter."

When the federal government first claimed ownership of the site, in 1973, Lang stopped paying the city rent for the property; she later argued that she had been operating on the site for so long that she had a legitimate claim to it.

Lang's longtime friend and adviser, John Chapman Gager, declared "a state of war" yesterday between the Old Town Yacht Basin and "the lawless City of Alexandria."

"You see that Berlin Wall they have erected down there?" he asked. "The Russians don't even do stuff like this any more."

"It's a shocker," said Lang. "They just seized the property without a writ of possession or anything. Other than that I have no comment."

Alexandria Mayor James P. Moran Jr. had a comment, though. "It's been a frustrating exercise in futility up until now," he said. "Katie Lang was simply a squatter."

After the federal government asserted its claim to ownership of the Old Town Yacht Basin site and 21 other waterfront properties 17 years ago, a federal judge upheld Lang's decision to stop the rent she had been paying the city. The judge ordered her to put $300 a month into an escrow account until ownership was resolved.

For a while she complied, but payments stopped in 1981, officials said. They said Lang still owes the city at least $21,000.

Gager said yesterday the lot brought in about $3,000 a month.

While the recent court ruling dismissing Lang's claim to the property elated city officials, Lang refused to be bound by it. She ignored a letter from the city attorney asking her to vacate the site by May 31. Last month officials handed out notices warning the 100 or so commuters who used the lot that any vehicles found there after June 30 would be towed and impounded.

"In the last five years, the city has probably given them {Lang and Gager} five formal notices to leave," City Attorney Philip G. Sunderland said. "In each instance, they refused to comply. The time has come."

On Thursday, eight-foot-tall signs were erected at the lot's entrances: "NOTICE -- PROPERTY OF THE CITY OF ALEX -- DO NOT ENTER."