A crowd of 200 people piled into a room at Pace University yesterday to testify at a public hearing of the Landmarks Preservation Commission on the proposed expansion of the Whitney Museum.

The hearing, which lasted all day, included testimony from the museum’s neighbors on the Upper East Side, politicians, and museum officials.

Critics of the plan focused on the demolition of two townhouses located south of the museum along Madison Avenue. Residents and preservation groups fear a precedent would be set of allowing the destruction of significant buildings in a designated historic district.

Supporters, including members of the local community board and museum officials from around the city, testified that the buildings’ demolition was a necessary part of the expansion.

The expansion, designed by the Italian architect Renzo Piano, involves a nine-story tower made of copper-aluminum alloy. It would nearly double the museum’s exhibition and public space to 124,000 square feet. At the top of the tower a loft-like space to house large-scale works would be built, with mechanical louvers on the roof working to allow sunlight to filter into the galleries. The tower and the original Marcel Breuer-designed building, separated by a 10-foot crevice, would be connected by a series of glass walkways.

To construct the museum’s new entrance, two townhouses on Madison at 74th Street would be razed.

“It will look like a broad smile with a tooth removed,” the president of the Coalition of Concerned Whitney Neighbors and a resident of 800 Park Ave., Don Gringer, told the city commission. “It will be the only block on the entire stretch of Madison Avenue from 59th Street to 96th Street that has a cut like this in the midblock.”

While one of the townhouses is not considered historically significant, the second building, at 941 Madison Ave., is classified as a “contributing building” in connection with the Historic District designation.

“Ingress and egress to and from the ‘new’ Whitney is going to be achieved by breaking the continuity of the street wall on Madison Avenue and on 74th Street. We feel this is totally inconsistent with the predominating historically residential character of the Upper East Side,” the co-chairwomen of the Defenders of the Historic Upper East Side, Elisabeth Ashby and Teri Slater, wrote to the commission.

Supporters of the plan argued the demolition of the two buildings was necessary. “From what I have learned of the Whitney plan, it is a modest proposal that carefully addresses such issues as visitor traffic, circulation, deliveries, and sidewalk congestion while accommodating the needs and varieties of contemporary art of the United States as well as the museum’s educational and public mission,” the director of the Metropolitan Museum of Art, Philippe de Montebello, wrote in a letter to the landmarks commission.