Judy Collins's voice will waft through the St. Mary's countryside Sept. 19 as the folk singer known for such 1960s classics as "Both Sides Now" performs an outdoor benefit concert to help preserve Sotterley Plantation.

Collins's appearance is a celebration of Sotterley's inclusion on the National Trust for Historic Preservation's "American Treasures" list earlier this year. The manor house, built about 1710, perches on a bluff overlooking the Patuxent River. In 1996, the National Trust named it an endangered historic site, and the plantation has since received more than $2 million earmarked for restoration efforts scheduled to begin in 2000.

Tickets for "Under the Stars with Judy Collins: In Celebration of an American Treasure" range from $28 to $38 and are available by calling 1-800-787-9475. Proceeds from the concert and concessions will go toward the restoration of Sotterley, Maryland's last surviving Tidewater plantation accessible to the public.

"We really wanted to find an artist sympathetic to preservation," said Carolyn Laray, Sotterley Foundation director.

Collins contributed to the album "Sing America," which was a benefit project to save historic American sites. She is also a friend of Robert Aubry Davis, the WETA radio host who will emcee the concert with Richard Moe, who is president of the National Trust and has a house in Calvert County. Laray said Davis was instrumental in getting Collins to commit to the Sotterley performance, where she will receive a fraction of what she normally charges for concerts.

Laray said baby boomers seem excited about the event even though their children may stare blankly as the Grammy-nominated artist's famous tunes are rattled off: Ever hear of "Chelsea Morning"? How about "Send in the Clowns"? Not even "Both Sides Now"? "[Collins] is popular with the songs-for-aging-children generation," Laray joked, referring to the WETA program of 1960s music co-hosted by Davis. "She's a voice they can identify with. Some of the younger folks just say, 'Who's Judy Collins?' "

Though they may not share the same nostalgia as their parents, children and teenagers should have plenty to enjoy at the performance, Laray said. Gates will open at 4:30 p.m. with tours of the estate and a warm-up show with local duo David and Ginger Hildebrand, who will bring Colonial music and song to the venue. Regional food and drinks will be on hand all night.

Visiting Sotterley is an educational opportunity for people of all ages, said William Dupont, an architect with the National Trust's historic sites operation. The mansion garnered national attention in 1996 when the great-great-granddaughter of a Sotterley slave joined the great-great-grandson of the slaveholder in a fight to save the estate. Sotterley is unique, Dupont said, because an original slave cabin and customs warehouse still stand on the grounds.

"A lot of people lived, worked and were enslaved at the site," Dupont said. "Their stories can be read about in textbooks . . . but to have that as physical, tangible evidence makes those stories all the more real. It helps us understand where we are today and where we're going."

CAPTION: Folk singer Judy Collins will perform at an outdoor concert Sept. 19 to benefit Sotterley Plantation.