BALTIMORE -- The evening's rain began to fall last weekend and darkened clouds hurried the arrival of another dusk. The aging sea wall of Fort McHenry, Baltimore's urban national monument and historic shrine, slowly faltered under the weight of an undetected shoreline attack.

Once, the peninsular stronghold withstood a much more severe siege from British naval power along the shores of the Patapsco River that inspired Francis Scott Key's "The Star-Spangled Banner." Yet even though the air is now quiet and the massive flag that is the trademark of this monument waves quietly, the fort is under attack from erosion caused by the Patapsco. The fort, renowned for its defense of Baltimore during the War of 1812, requires massive reinforcement -- in the form of an $11.5 million renovation. Private and federal organizations have answered the clarion call, and a fund-raising effort targeted for national exposure is under way.

At several points along the sea wall, parts of the structure have eroded and full capstones have fallen into the river's edge. Markers placed by the National Park Service discourage visitors from nearing the unstable sea wall, but officials still worry that hazards exist.

The Patriots of Fort McHenry, a private group founded three years ago by business and civic leaders intent on improving the park, has raised $75,000 for projects that include enlarging the park's visitors' center and restoring grounds and facilities to their condition during the War of 1812, officials said.

At the same time, the National Park Service, which operates the fort, will spend $750,000 to rebuild the bulk of the sea wall, which stretches 3,713 feet around the fort.

Paul Plamann, director of public information at Fort McHenry, said 800,000 people visit the park each year, although only 250,000 tour the visitors' center.

"What happens is that many people just visit to enjoy the open air and greenery of the park, and less than half the people that come really appreciate the historic significance of the fort," Plamann said.

He added that Fort McHenry is such a common field trip for schoolchildren that 20 school buses might crowd the parking lot on any afternoon.

"People use {the fort} as you would any nice place to be," said Plamann, who calls the park "a green oasis in the concrete jungle of the city."

"People bring their lawn chairs and come just to watch the sailboats, or they bring their picnic gear for a nice sunny afternoon. This place has a lot more than just historical appeal.

"We're in a unique position," he said. "We're a historical park surrounded by commercial and suburban developments; the park benefits from such exposure, and visitors benefit from such accessibility."

The problems with the fort became apparent to community groups, such as the Disabled American Veterans, with longtime ties to the park. Some of their members established the Patriots.

Patriots President Walter Hyle said, "We saw the {need for} renovations were plenty and not going to be taken care of by the federal government," which did not have funds available.

Initially, the Patriots delayed its fund-raising efforts to avoid competition with the Statue of Liberty's restoration, which was completed in 1986.

Plamann said the Patriots plan to follow the Liberty group's lead of using Lee Iacocca to publicize the campaign to restore the New York statue by adopting identifiable spokesmen for their own national campaign.

Several people have been suggested, Patriot board member Brent Kansler said, but no decision has yet been made.

Kansler and other Patriots are confident their goal of roughly $11.5 million is not unreasonable. They plan to reach both corporate and individual donors.

"We estimate that about 80 percent of the money will come from 20 percent of the donors and about 20 percent of the money will come from 80 percent of the donors. In other words, most of the money will come from big organizations and businesses," Kansler said.

"Still, it's very important to us to attract the large numbers of small donors because what we're really seeking is exposure to a lot of people."