The first time Celeste Morello succeeded in getting a Roman Catholic church mural listed on the city's historic register, the Archdiocese of Philadelphia issued a statement applauding the news.

Emboldened, Morello filed another nomination in December to protect a group of important paintings in the Cathedral Basilica of SS. Peter and Paul.

But this time, her efforts did not go over so well.

On Jan. 7, the archdiocese responded by sending a stern letter to all parish priests warning them not to cooperate with preservationists, and to report any attempts by "independent parties" to landmark church property.

The directive, signed by Monsignor Daniel J. Kutys, a top diocesan administrator, goes on to assert that the city's historic preservation law is an infringement on religious freedom, as well as a financial burden, and vows "to challenge the current attempts to have various church properties designated as 'historic.' " The letter puts the word historic in quotation marks each time it is used.

The directive has angered and alarmed Philadelphia's preservation community at a moment when the city's surplus religious buildings are becoming increasingly vulnerable to sale and demolition.

"It's very unfortunate" to see the archdiocese take this stand, said Patrick Grossi, the advocacy director for the Preservation Alliance for Greater Philadelphia. The letter makes it seem that "these designations are done over the wishes of the parishioners, when in fact the parishioners are usually in favor of them."

The archdiocese has long been wary of listing its buildings on the historic register, fearing that landmark status will make its shuttered churches less valuable and more difficult to sell. In the last few years, it has tangled with preservationists over the protection of such high-profile sanctuaries as St. Laurentius in Fishtown and the Church of the Assumption in the Loft District. It lost both battles.

While the arguments in Kutys' letter are largely a restatement of the archdiocese's 2010 policy on preservation, the forcefulness of its tone is new. It specifically singles out historic nominations written by Morello and Oscar Beisert, two of the most active preservationists in the city.

Beisert's nomination helped rescue St. Laurentius at the eleventh hour, just as the archdiocese was preparing to sell the church to a developer as a teardown. Morello was instrumental in winning designation for an 1886 mural by Filippo Costaggini at Old Saint Joseph's church in Society Hill. It was only the second time that the city had landmarked a work of sacred art.

Unlike some cities, Philadelphia does not require the property owner's consent before a building's designation is changed, even though that means the exterior cannot be altered without Historical Commission approval. Despite the archdiocese's assertions, the courts have affirmed the right of cities to protect church property, according to Tuomi Forrest, a vice president at Partners for Sacred Places, a national preservation organization headquartered in Philadelphia.

"The bottom line," Beisert said, "is that they don't want anyone telling them what to do with these properties."

In an email, Kenneth A. Gavin, the archdiocese communications director, downplayed the importance of the Jan. 7 letter, saying it "does not signal blanket opposition on the part of the archdiocese to historic preservation." Gavin said the letter was simply a reminder to pastors to seek diocesan approval.

Because of the city's frenzied housing boom, religious buildings have become immensely desirable as teardowns by developers, especially if they occupy large sites that can support a group of rowhouses. As congregations have dwindled, many of the city's great stone churches and synagogues are sitting empty or neglected. The archdiocese has been especially eager to get its unused buildings off the books.

Thomas Rzeznik, a professor of American Catholic history at Seton Hall University, said the surplus had become an especially difficult issue for the church.

Ideally, it should be spending its resources on serving the community rather than on building upkeep, he said. Yet there is no denying that its older buildings are an emotional touchstone, especially in places like Philadelphia, where people identify their neighborhood by their parish.

"The archdiocese policy in Philadelphia tracks closely with what's happening in Chicago," Rzeznik noted. After several preservation battles there, the archdiocese persuaded Chicago to loosen its preservation law. The archdiocese's consent is now required before a religious building can be landmarked.

Morello would hate to see that change in Philadelphia.

"I don't think the people in the archdiocese really care how people like me feel about these buildings," she said.

She is now trying to get the Historical Commission to designate St. Charles Borromeo, the immense brownstone church in the Graduate Hospital area, and Constantino Brumidi's paintings at the Cathedral. Brumidi did those canvases in 1864, after completing frescos for the Rotunda of the U.S. Capitol. "If people knew that, I'm sure they would dig deeper and give more money to the church," Morello said.

The Historical Commission's director, Jonathan Farnham, declined to comment on the letter.