With another sale in the offing and the fate of the celebrated Boyd Theater uncertain, the National Trust for Historic Preservation has placed the art deco movie palace on its annual list of the 11 most endangered historic sites in America.

The sad, yet nevertheless coveted, designation comes at a low moment for the shuttered 2,350-seat Chestnut Street theater. Only three years ago, Live Nation, a subsidiary of Clear Channel Communications Inc., purchased the rundown Boyd with the intention of turning it into a sumptuous venue for musical shows. But the company, which has been consolidating operations, decided to get out of that business and put the property back on the market.

Live Nation has invited interested parties to submit bids for the property by Friday. But there is no guarantee that a buyer would be committed to restoring the ornate interior for live theater performances or for film. The building at 1908 Chestnut St., which was constructed in 1928 and is the last intact movie palace left in Center City, does not have historic protection in Philadelphia because of its entanglement in a lengthy legal battle dating from the 1980s.

That's why the National Trust decided to single out the Boyd this year, trust president Richard Moe said, along with such other threatened locales as New Orleans' Charity Hospital and Manhattan's Lower East Side neighborhood.

"The nomination helps bring real attention to these sites, both locally and nationally," Moe explained. "We hope it will bring the theater to the attention of a potential developer."

When Live Nation acquired the Boyd from the Goldenberg Group in 2003 for roughly $13 million, the company was seen as the theater's savior. It promised to invest about $17 million to expand the small stage for live shows and to buff up its elaborate art deco detailing, which includes a series of etched mirrors and murals depicting the history of women, and an intact marquee and ticket kiosk, all designed by the noted theater architects Hoffman & Henon.

But costs escalated, and public support from the city and state never materialized.

Live Nation did manage to stabilize the building, sealing it from water infiltration, and obtained rights to an adjacent parking lot before giving on the restoration project, said Adrian Scott Fine, the trust's Philadelphia-based program officer and a member of Friends of the Boyd, a non-profit devoted to finding a sympathetic reuse for the theater.

Fine said the group isn't "sure what to expect" from potential buyers. Although Friends of the Boyd has been contacted for information by several preservation-minded investors, it's not clear that they will be able to put together a winning bid.

"It's a highly challenging building," Fine acknowledged. "It's why we lobbied to have it listed. More than ever, the Boyd is at a crossroads."

One factor that might help the Boyd is a no-competition clause in Live Nation's sale invitation. It precludes the future owner from converting the theater into a venue for rock concerts, a business Live Nation still pursues.

At the same time, the clause could encourage some buyers to eye the site for a high-rise and retail development. Last year, the Irish firm Castleway Developments paid more than $36 million to acquire the parcel immediately to the south for a luxury condo and hotel development.

In the hope of drumming up support for preservation, Friends of the Boyd plans a rally in front of the theater Thursday from 11:30 a.m. to 1 p.m., said Howard Haas, the group's president.

The Boyd's expansive auditorium, with its curving balcony, is considered too large for today's movie industry, which prefers to market films to smaller, niche audiences. Three small screening rooms that were once part of the Boyd have already been turned into shops.

As a live theater, the Boyd would have to compete with the state-supported powerhouses along Broad Street's Avenue of the Arts, including the Academy of Music and the Kimmel Center.

Still, cities around the country have found creative strategies to preserve their historic movie palaces. In New York, AMC Entertainment Inc. moved the historic Empire Theater 168 feet down 42d Street, then built a 25-screen multiplex onto the top of the façade.

The National Trust's Moe said he remains optimistic about the Boyd, noting that of the 200 places listed by the trust in the last 20 years, only seven have been lost.

The Boyd was chosen for this year's list from among 100 nominees. Along with Charity Hospital and the Lower East Side, the other endangered properties listed are: California's state parks; the Great Falls Portage on the Lewis and Clark trail in Montana; Hangar One at Moffett Field in Santa Clara County, Calif.; Chicago's Michigan Avenue streetwall; Buffalo's Peace Bridge neighborhood; Dallas' Statler Hilton Hotel; Sumner Elementary School in Topeka, Kan., and the Vizcaya and the Bonnet House in Florida.

Contact architecture critic Inga Saffron at 215-854-2213 or isaffron@phillynews.com.