Well over a year ago, officials at the Preservation Alliance of Greater Philadelphia were pondering the national significance of the city's outsize and unique cache of branch libraries built at the behest of philanthropist Andrew Carnegie in the early 20th century.

Carnegie's renowned building project - considered by scholars a transformative program for American libraries and public education - led to construction of 25 branch buildings here, of which most survive. Only New York City boasts more.

John Gallery, head of the alliance, contacted the Historic American Buildings Survey, or HABS, a National Park Service program, and a meticulous study was launched of the 20 or so remaining Carnegie libraries.

"I never presumed they would cease to be libraries," Gallery said in a recent interview. "That thought never crossed my mind."

But that was before the subprime meltdown and the decline of city finances. Now the Nutter administration has proposed closing 11 branch libraries, including four of the original Carnegie buildings - Logan, Holmesburg, Haddington and Kingsessing.

And the Preservation Alliance has decided that those four buildings are too important for the city - and the nation - to lose.

With the 11 closures scheduled for the end of this month, Gallery is pushing forward with an application to have the four threatened Carnegie libraries certified as historic by the Philadelphia Historical Commission.

"It is our intent to try and submit nominations to the Historical Commission . . . as quickly as we can," he said earlier this week. "And we're looking into what's involved in submitting them . . . for the National Register" of Historic Places.

Doug Oliver, Mayor Nutter's spokesman, said the city had not determined what would happen to any of the 11 libraries slated to close. There are no firm plans to sell, lease, reuse or mothball them, he said.

"With respect to the issues related to ownership, as well as the requirements of the deeds, the law department is reviewing it," he said. "This review of ownership and deed requirements will feed into a cross-department group which will determine what will happen to the building."

Oliver added that library officials are convening "community roundtables" to help decide what the buildings might be used for in the future.

For Gallery and other preservationists, the disposition of the Carnegie-built properties presents issues that go far beyond "deed requirements," although the Carnegie-built Holmesburg branch is apparently owned by the trustees of Lower Dublin Academy, according to a 1907 deed. When it ceases to be a library, the building reverts to its owners, the deed stipulates.

"The Philadelphia Carnegies are your quintessential Carnegie libraries," said Catherine Lavoie, the historian with the National Park Service in Washington who conducted the intensive study of the city's buildings last year.

"The Carnegie-funded branch libraries are important cultural resources and should be preserved," she said. "They refer to the city's early commitment not just to libraries but to public education."

Lavoie said the city's Carnegie collection was built from 1905 to 1930, and represents virtually the entire span of Carnegie's effort.

The philanthropist believed that access to information and education held the key to success - the free library was the seedbed of the American Dream; his famous program led to construction of about 1,600 libraries across the country.

The libraries were not simply gifts, however: Municipalities had to actively embrace the program, providing building sites, books, and 10 percent of the operating costs.

"It was a grassroots movement," said Lavoie. "That's one of the reasons these are so important. They made local municipalities buy into the concept."

Philadelphia definitely bought in, she said.

Before the Carnegie program there were no free library buildings in the city that had been expressly built for that purpose. Books were shelved in old houses and in storefronts. Carnegie - and to a great degree Philadelphia - changed that.

Lavoie said that the city's Carnegie libraries, mostly simple beaux arts structures, were largely designed in response to the needs expressed by turn-of-the-century librarians. That, she said, makes their interiors, laid out to serve the needs of readers and librarians, as significant as their exteriors.

Because the interiors are so important, they present a nettlesome issue for preservationists here. As currently written, the city's preservation ordinance protects the exterior of structures but does not bar sales or interior changes.

"We can be concerned about the buildings as physical objects and protect their exteriors," said Gallery. "Is that enough?"

Lavoie believes the interiors, so important in library development, are absolutely an integral part of the buildings' historical significance.

Gallery said the "interiors are exploring ideas about how you make information available to the general public."

A bill that would extend the authority of the Historical Commission to interiors is being considered by City Council but has not been brought to the floor for a vote.

If the city decides to sell or lease those library buildings it can, Gallery and other preservationists are also concerned about building deterioration during what promises to be a lengthy sales period.

The city holds historically certified buildings for sale - old Germantown Town Hall is a case in point - that are in bad physical condition and deteriorating daily.

"These libraries are in such good shape now, but if you turn the heat off and leave them vacant, it doesn't take long for them to go downhill," said Lavoie.