The walls that saved Baltimore from the British now need to be saved themselves.

And soon they will be: Congress has allocated $3 million to restore the cracked and crumbling brick walls of Fort McHenry, the military bastion where U.S. troops repulsed a British naval attack on Baltimore in 1814 and a young lawyer named Francis Scott Key was so moved that he wrote "The Star-Spangled Banner."

Set to begin next month, the three-year project will be the most comprehensive reconstruction of the famous "star fort" since the 1930s, when the Army turned the South Baltimore landmark over to the National Park Service.

The work will take nearly as long to complete as it took to build the fort and will require 250,000 new bricks, custom-made in 13 variations to blend with the ones visitors see today. That's the biggest brick order for a Baltimore project since Oriole Park at Camden Yards, which took 600,000.

According to National Park Service representatives, the restoration is needed to prevent the fort from crumbling. (The work is being staged so that the fort won't have to close to the public, and it is not expected to harm attendance.)

Park Service officials say it will help the fort maintain its historic integrity in an era when it is increasingly difficult to distinguish between reality and reproduction.

"This is the original fort," said its superintendent, John W. Tyler. "It's part of our national heritage. It's the only site in the country that has been designated both a national monument and an historic shrine. You could make a fort out of plastic, but it wouldn't be the same thing."

There's no other fort like it in the country because of the star-shaped configuration of the walls, said park historian Scott Sheads. "It's considered the finest example of fort design in North America,"he said. "That's what brings all the schoolchildren here."

Rep. Benjamin L. Cardin, D-3rd, whose district includes the fort, was instrumental in securing repair money as a line item in the federal budget.

"Fort McHenry is a symbol of our struggle for freedom, and we must not let it deteriorate," he said. "It's a national treasure. I'm delighted that the restoration is finally getting under way."

To the 600,000 visitors a year who make Fort McHenry one of Baltimore's busiest tourist attractions,the deterioration may not be easy to spot from a distance. "It's only when you get up close that you can see that the work is needed," Mr. Tyler said. "But two of the walls are near collapse."

The chief problem, he said, is that the 13-foot-high walls were repaired incorrectly 60 years ago, when preservation techniques were less sophisticated.

In the 1930s, he explained, joints between the bricks were repointed with Portland cement, a mortar that dried to be harder than the bricks. During the freeze-thaw cycle of winter, he said, the mortar and the bricks expand and contract at different rates, and the bricks tend to crack while under compression.

In addition, Mr. Tyler said, the walls don't drain well. Rainwater collects behind them, causing sections to bulge out and ground salts to seep through cracks, discoloring the bricks.

On a recent tour of the fort, Mr. Tyler pointed out numerous jTC areas where bricks have popped out of the wall, leaving unsightly gaps. Near the top, sections of the wall have shifted or developed fissures, and capstones are coming loose. Limestone quoins, or corner piers, are crumbling and need to be repaired or replaced.

For two years, architects and archaeologists have been working with park service restoration experts to determine the best way to restore the fort. Their recommended solution entails two basic actions: replacement of broken or missing bricks and replacement of the Portland cement with a mortar that is softer than the bricks.

For the most part, contractors will not replace entire walls but will patch smaller areas that need repair. In some cases, however, entire wall sections will be taken down and rebuilt so that a new drainage system can be installed. Some of the outer battery walls beyond the fort's perimeter also will be repaired.

"It's all handwork," Mr. Tyler said. "You can't have a machine do it. I would think this is one of the most complex restoration projects in the country, one that requires very delicate handling because of the nature of the place."

Grieves Worrall Wright & O'Hatnick of Baltimore is the lead architect for the project. Partner David Wright headed a team that photographed all 104,520 square feet of the fort's exterior wall surface to pinpoint areas that need repairs. New London Brick Works of Salisbury, N.C., is the brick manufacturer.

Mr. Tyler and Mr. Sheads said the goal is to retain as much of the original wall surface as possible and to make repairs only where needed. Even with the attempt to use compatible replacement bricks, they said, the repaired areas will stand out from those that are not altered because the older bricks have a "patina from age" and often have moss or lichen growing on them.

The difference in appearance is appropriate, they say, because the fort's walls were built over time and have always had a "patchwork" appearance. "I compare it to a house," Mr. Sheads said. "You don't need to fix the whole house. You only need to fix where something goes wrong. The fort is the same as a house, a very big house."

Mr. Tyler said up to $1.5 million more may be needed to complete repairs, but he is optimistic that additional funds can be secured as part of the park service's capital budget.

This is the 200th anniversary of the year Congress allocated funds to build Fort McHenry as part of the nation's defense against enemy invasion resulting from the war between France and England. Construction began in 1798 and continued until 1802. It cost $95,073.12 -- more than twice the 1799 estimate of $39.938.34.

The 1814 Battle of Baltimore is commemorated at the fort each year on Defender's Day, in September.

The fort was named for James McHenry, a Baltimore resident who served as secretary of war under Presidents George Washington and John Adams.

Mr. Tyler said the federal government must continue to play a lead role in preserving what's real in America so that it doesn't get lost amid the fabrications.

In Northern Virginia, by contrast, the proposed historical theme park known as Disney's America has drawn criticism from preservationists and others for threatening to blur the lines between fact and fantasy in the public's mind.

"There are certain things around the country that we've decided to save, including the Liberty Bell, the Statue of Liberty and Fort McHenry," Mr. Tyler said. "It isn't done for economic development. It's done because they're part of our American heritage."

Fort McHenry doesn't have the "epic proportions" that characterize some monuments, he said. "But people read about it and come to see that it's still here. It's important to go back and touch history every once in a while as we move on."

FLAG DAY

It's hand-over-heart time again at Fort McHenry. The Pause for the Pledge of Allegiance celebration, held every Flag Day, starts today at 7 p.m. at the South Baltimore landmark, to be followed by fireworks.