The weathered planks and sharp angles of tobacco barns have shaped the Southern Maryland landscape for centuries. Now, with the barns falling down from neglect or razed for development, a national preservation group has designated them among the nation's most endangered historic places.

The nonprofit National Trust for Historic Preservation yesterday included the tobacco barns of Calvert, Charles and St. Mary's counties, as well as those in Anne Arundel and Prince George's, on its annual list of endangered sites. Also on the list: a shuttered Pennsylvania mill that forged steel to build the Golden Gate Bridge and the Empire State Building; a California ranch that was the final home of the legendary racehorse Seabiscuit; and the entire state of Vermont, in an effort to block the expansion of Wal-Mart stores there.

National Trust officials said being on the list is no guarantee of survival, but it improves a site's chances of getting preservation grants and other funding and challenges people to come up with creative ideas. Since the list started in 1988, only one site -- the Mapes Hotel in Reno, Nev. -- has been wiped out completely, the organization said.

"That's incredible -- that's terrific," said Teresa Wilson of St. Mary's County, who asked preservationists in Southern Maryland to help her nominate the barns. "We were on the edge of our seats."

Richard Moe, president of the National Trust, owns a weekend home in Calvert County. He acknowledges a soft spot for the barns, some of them collapsing into little more than a heap of rough wood, a few others well-maintained with their silhouettes freshly painted red. He said he's always finding another one, on some winding back road, that he has never seen before.

"I think more than any other thing, they define Southern Maryland's rural nature," he said. "That's what people love about the place."

Tobacco had been the heart of Southern Maryland agriculture since the 17th century. The farms sprawled across the landscape with their drafty, open barns designed for air-curing the leaf. But since 2001, a state-sponsored buyout program for tobacco farmers has transformed those farms, as owners switch to other crops.

So for now, thousands of barns drift into obsolescence, some used for storage, some empty and battered by wind and rain. When the land can be sold and developed -- under the buyout program, it must be kept for agricultural uses for a decade -- the barns will face a more immediate crisis.

Because the barns face a variety of threats, from bulldozers to termites, there won't be any single solution, Wilson said. She and other preservationists say they have plans: They'll apply for grants and they hope to start a fund to pay for renovating or moving barns. They'll spread the word through a Web site, perhaps, and raise awareness through a photography or other art exhibit. They could send information to farm owners about ways to keep their barns standing.

Other local sites have benefited from the National Trust's list. In 2000, Abraham Lincoln's Retreat in Northwest Washington was listed as endangered. Since then millions of dollars have been raised, and restoration began this winter. The Chesapeake Bay Skipjack Fleet was listed in 2002; only 15 of the boats designed for oystering were left on the bay.

The National Trust brought visibility and fundraising help to the Chesapeake Bay Maritime Museum in St. Michaels, Md., which now has the money to pay for an apprenticeship program, said John Valliant, president of the museum. "It's been a tremendous help," he said.

National Trust officials said the list this year includes several places that are facing immediate risk. The abandoned wooden buildings of the Elkmont Historic District in the Great Smoky Mountains National Park in Tennessee could be demolished. The owner of the Madison-Lenox Hotel in Detroit wants to knock it down for a parking lot. Historic Cook County Hospital in Chicago could be taken down, too.

Some sites, such as the tobacco barns, are fading through neglect. The Bethlehem Steel Plant, later known as Bethlehem Works, a symbol of the country's industrial age, is rusting away in Pennsylvania. Ridgewood Ranch in California, Seabiscuit's final home, is in trouble because its owners don't have the money to take care of all the buildings, the National Trust said.

The barns are Moe's favorite this year, he said. "You can't save every single one of them," he said, "but we want to raise public awareness of the threat to these barns so people who own them will take steps to preserve them, and others will want to help."

Since the 17th-century Maryland barns, like Stephen Reeves' in Chaptico, were used to cure tobacco. Years of weather have not been kind to this old tobacco barn -- or the Old Glory attached to its side -- in a field off Route 5 near New Market. Preservationists hope they'll be able to spread the message that these historic structures should be saved for future generations.