Following through on a threat, a developer says he’ll begin scraping the architecturally significant elements off the facade of his building on East 9th Street as early as tomorrow – defying a decision yesterday by the Landmark Preservation Commission to designate the vacant school as a historical landmark.

The developer, Gregg Singer, claims the landmark designation is not based on the building’s merit, but is part of a campaign by the Bloomberg administration to block development on the site as political payback for a supporter.

Mr. Singer said Mr. Bloomberg “is trying to use landmarks to stop development, and that is illegal. He is using Soviet-style tactics and doing what he wants with no regard for the law.”

Mr. Singer was consulting with his team of lawyers yesterday and did not attend the commission’s hearing. The designation requires final approval by the City Council, but Speaker Christine Quinn already gave her support to the landmarking.

In 1998, Gregg Singer and a group of unnamed investors purchased the former home of P.S. 64 for $3.15 million from the city. If yesterday’s designation holds up in court, Mr. Singer said it would cost him $36 million – the value of the building’s 120,000 square feet of air rights.

Last month, Mr. Singer sued the city for $100 million, claiming it was interfering in the development of his property. The suit claims that Mr. Bloomberg “manipulated City agencies like marionettes to concoct ways to prevent” Mr. Singer and his investors from converting the property into a dormitory.

The suit says that Mr. Bloomberg “cut a dirty political deal” with a former City Council member, Margarita Lopez, to block the proposed development in exchange for her endorsement in the last mayoral election. Ms. Lopez was a strong opponent of Mr. Singer’s in his previous attempt to prepare the building for development. Mr. Singer’s lawyer is a former deputy mayor for the Giuliani administration, Randy Mastro.

A lawyer with the city’s law department, Gabriel Taussig, said the allegations are “absolutely without any merit.”

“We intend to vigorously defend the city’s position in the litigation,” Mr. Taussig said yesterday.

Yesterday, landmarks commissioners cited a variety of reasons for the designation, including the French Renaissance revival-style architecture and the famous New Yorkers that attended the school, including a songwriter, Yip Harburg, and a director, Joseph Mankiewicz. Several commissioners said the building was a centerpiece of a grassroots political movement in the 1960s and 1970s that sought to revitalize neglected urban neighborhoods through community involvement.

Commissioner Roberta Gratz called the Giuliani administration’s decision to auction the building “sheer folly.”

“P.S. 64 is not only a New York City landmark,” Ms. Gratz said. “It is a national landmark in the post-World War II struggle to save American cities.”

“Designating P.S. 64 won’t by any stretch of the imagination stop development on the Lower East Side; it will, however, stop inappropriate development and make the appropriate and beneficial possible,” Ms. Gratz said.

The commission’s landmarks designations have never been overturned by courts. A spokeswoman for landmarks, Elisabeth de Bourbon, noted that a number of city-owned buildings across the city have been auctioned off to private owners and subsequently landmarked.

She said that a preliminary search showed that P.S. 64 was not considered for designation as a landmark when it was auctioned off by the city in 1998.

Preservationists hailed yesterday’s designation as significant for its consideration of the cultural history of the building, in addition to its architectural merits.

The director of the Greenwich Village Society for Historic Preservation, Andrew Berman, said: “In the ’60s, things that related to immigrant history and the working class were generally shunned by the commission. These days, they are more willing to look at those things.”

The building has sat vacant since 2001, when a court evicted a popular Latino community center called Charas/El Bohio, inciting large community protests.

For Mr. Singer to use the lucrative air rights over the vacant school, the building must be available for community facility use, according to the deed. After a series of earlier designs, Mr. Singer has most recently proposed developing a 19-story dorm in the back of the building, preserving most of the building’s historic facade. Mr. Singer said he has tried winning the community’s and the city’s support through other incentives – including a share of profits – to no avail.

A local filmmaker who attended yesterday’s hearing, Roland Legiardi-Laura, said a dorm would destroy the neighborhood. He said Mr. Singer had a right to build, but that he should do so “ethically” and “with sensitivity to the community.”

“We hope he will reach a logical epiphany,” Mr. Legiardi-Laura said. “What will you gain right now by stripping the building?”

Mr. Singer said that without the architectural details, a judge would be more likely to reverse the commission’s decision.

“The law says you can not landmark to stop development,” Mr. Singer said. “A judge will look at the building and say there is nothing redeemable about the building.”

City Council Member Rosie Mendez, who succeeded Ms. Lopez in January, said she would not be concerned if Mr. Singer moves ahead with selective demolition of the building’s facade. She considers it a victory because the “building has been saved.”

Ms. Mendez said she would work toward opening up the facility for community use. She acknowledged that could mean acquiring the building from Mr. Singer, who has said it would cost $86 million to do so.

“Maybe we will get an angel,” Ms. Mendez said.