rguing that significant buildings are not getting their due, advocates of midcentury architecture are stepping up pressure on the city's Landmarks Preservation Commission to hold full public hearings on proposals to raze two movie theaters on the Upper East Side of Manhattan.

Plans have been announced to convert Cinemas 1, 2 & 3, a 1962 International-style theater on Third Avenue across from Bloomingdale's, into retail space. The Beekman, a 1952 late Streamline Moderne design at Second Avenue and 66th Street, is to be replaced by a breast and diagnostic imaging center run by Memorial Sloan-Kettering Cancer Center. The theater is scheduled to be closed down this summer.

On another front, a lawsuit was filed against the city last week in New York State Supreme Court seeking to prevent reconstruction of 2 Columbus Circle into the Museum of Arts and Design. The marble-clad building with a "lollipop"-motif facade by Edward Durell Stone once housed Huntington Hartford's Gallery of Modern Art. The landmarks commission has never held a public hearing on the future of the building, on which demolition is expected to begin in late May.

These two different battlefronts represent a larger argument on the part of preservationists that the commission has generally neglected postwar architecture and been unresponsive to their concerns about Modernist sites.

"The commission ought to hear the arguments and let them be debated in a public forum - that's democracy," the architect Robert A. M. Stern, who is active in preservation issues, said in an interview.

But Holly Hotchner, director of the museum going into 2 Columbus Circle, said, "There are no landmarks hearings on many buildings."

Friends of the Upper East Side Historic Districts, a group that is spearheading opposition to the alteration of the movie theaters, said in a statement: "These insensitive and destructive actions highlight the urgent need to protect the Modern architecture on the Upper East Side and across the city. The Landmarks Preservation Commission has designated some important Modern buildings, but most remain at risk."

John Jurayj, co-chairman of the Modern Architecture Working Group, an advocacy organization, said at a commission hearing last week on the Jamaica Savings Bank in Queens, itself an example of mid-20th-century architecture: "Modern preservation is in a major crisis in our city, a crisis that is shortly going to get worse unless the Landmarks Preservation Commission starts to act more aggressively."

At the same meeting, Kate Wood, the executive director of Landmark West, a community group focused on preservation on the Upper West Side, reproved the commission for not putting the fate of 2 Columbus Circle before the public. "If the Landmarks Commission held a public hearing for 2 Columbus Circle, literally hundreds of people would attend and testify - both for and against designation," she said. "The question is, what more will it take?"

Diane Jackier, a spokeswoman for the commission, said: "All of the preservation advocacy groups say the commission is slow to respond. The commission balances the concerns of advocacy groups across the city with our own interests."

Robert B. Tierney, the commission's chairman, was traveling out of the country this week and unavailable for comment, Ms. Jackier said.

To be sure, the commission's work has been hampered in part by a low annual budget - $3.5 million - and staff cuts over the past decade. The Modern Architecture Working Group acknowledges these handicaps but has urged the commission to step up designations of sites as landmarks. Last year, the commission designated 12 individual landmarks and 3 historic districts, which Ms. Jackier said amounted to a total of 220 buildings, compared with 25 individual landmarks and 2 districts amounting to 261 buildings in 2000.

The group has also asked the commission not to give building owners too much advance notice of hearings on their landmarks. Otherwise, the preservationists argue, owners may pre-emptively alter the buildings.

Preservationists had repeatedly asked for hearings on the 1961 Summit Hotel on Lexington Avenue and the 1949 Paterson Silks Building at Union Square, both designed by the Miami architect Morris Lapidus. Hearings were finally scheduled, but not until demolition had begun on the Silks Building.

The fight over 2 Columbus Circle has intensified since the city agreed to sell the nine-story building to the Museum of Arts and Design in June 2002, for $17 million. The museum, now on West 53rd Street, plans to reconstruct it for about $30 million according to a design by Brad Cloepfil of Allied Works Architecture. Construction is expected to begin by the middle of this year and to be completed in mid-2007.

Some call 2 Columbus Circle ugly and say they would just as soon see it go. But many Modernists argue that the 1964 building is an important example of postwar architecture. "It is a building that should be saved; it's still not too late," said Mr. Stern, the architect. "Under any definition of what a landmark is - culturally, physically and geographically - this is a landmark."

The lawsuit filed last week was brought by property owners in the Parc Vendome Condominiums near Columbus Circle and by Landmark West. It aims to block the sale on the grounds that it was conducted without due process in violation of the New York State Constitution, the New York City Charter, the General Municipal Law and New York's public trust doctrine.

Ms. Hotchner said in an interview yesterday that the lawsuit "in no way affects our interest in going forward" with the museum and called it "an example of abuse of the legal system to subvert the public process."

Preservationists opposed to the building's renovation have already been to court on the project. Supported by the National Trust for Historic Preservation, the plaintiffs challenged the environmental review of the project and the failure by the landmarks commission to hold a public hearing on it.

In February, a five-judge panel of the Appellate Division of State Supreme Court unanimously upheld an earlier dismissal of that lawsuit.

Landmark West argues that its recent lawsuit would not have been necessary had the landmarks commission held a hearing as requested. "It's because they've refused to deal with this that we've had to resort to the courts," said Ms. Wood of Landmark West.

The commission's designation committee has said that no public hearing was ever held because it determined in 1996 that landmark status was not warranted for 2 Columbus Circle.

But several people who work in architecture or preservation have continued to appeal for a hearing, arguing that the commission was wrong to shut off public debate.

Last October, in testimony before the City Council subcommittee responsible for landmark preservation, Beverly Moss Spatt, a former chairwoman of the commission, described the commission as "totally isolated and in total disregard for public opinions."

Anthony M. Tung, a former member of the commission, told the subcommittee that the public was "being barred in numerous improper ways from a process which the council in its wisdom designed to be open and participatory."

In November, a coalition of civic organizations produced a report, "Problems Experienced by Community Groups Working With the Landmarks Preservation Commission," that detailed their complaints and suggested areas for change.

Friends of the Upper East Side describes Cinemas 1, 2 & 3 as the first "piggyback" duplex movie theater in the United States - "a significant milestone in the development of movie theater design."

The group cited the glass corner on East 66th Street and the ribbon windows on East 65th Street as examples of the International-style design "enlivened with a tilted glass facade and sloping streamlined lounge ceiling that refers stylistically back to the Moderne style of the 1930's."

But it also noted that the theater had already undergone extensive alterations of its exterior, including the replacement of Venetian tiles with a white stucco wall. In addition, the Upper East Side group says, important artworks in the interior have been removed, including an abstract oil painting by the Russian-born artist Ilya Bolotowsky, a geometric mural by Sewell Sillman and copper leaf-shaped chandeliers from Denmark.

Friends of the Upper East Side says the theaters are two of the few remaining art film houses in Manhattan. "We've lost almost all of them," said Seri Worden, the group's executive director.

Mr. Stern, the architect, said the issue was not merely the theaters' architectural value, but their contribution to the neighborhood's character. "They provide a layer of the past in relation to new things," he said.