NEW YORK - The United Nations has been one of New York's most recognizable landmarks, a sleek, modern slab standing tall above its more modest-sized neighbors along the East River.

But now a proposal calls for seven slender glass towers several blocks south of the U.N. complex that could dwarf the 39-story Secretariat - and residents say it would strain the largely residential neighborhood.

The city is being asked for zoning changes that would be needed for developer Sheldon Solow to realize his dream of a five-million-square-foot project on the 8.7-acre site of a decommissioned Con Edison power plant.

The property along First Avenue between East 35th and East 41st Streets is Manhattan's largest privately owned, undeveloped piece of real estate. The U.N.'s southern boundary is 42d and First.

Solow recently bowed to neighborhood pressure by agreeing to provide space for a public school, to set aside some apartments for moderate-income residents, and to lower the height of the tallest building from 864 to 721 feet, or 69 stories. The steel-and-glass U.N. Secretariat is 505 feet.

That might not be enough.

"We would like to see significant changes to the plan," said Councilman Daniel Garodnick, who represents the area.

State Sen. Thomas Duane said the buildings "are still too high and inappropriate for the neighborhood, where most buildings reach only as high as 40 residential stories."

The lawmakers were among a half-dozen officials who testified against the proposal last week at a Planning Commission meeting.

The developer's company issued a statement saying it looked forward "to continuing discussions with community residents and elected officials in our effort to be responsive."

Besides the Secretariat, which was completed in 1952, the neighborhood includes Tudor City, a historic district of 12 brick-and-stone apartment buildings built in the 1920s.

Solow's project would contribute to a New York building boom projected to include five skyscrapers at the World Trade Center site and up to 24 million square feet of office space on Manhattan's far West Side - plus luxury condos seemingly sprouting in every neighborhood.

It would have 4,172 apartments, a 1.38-million-square-foot office building and a public pavilion.

Solow did not address the Planning Commission, but his architects said the towers would enhance the skyline.

"This plan is fundamentally about claiming a former industrial site and turning it to the use of people, activities, open space and mixed-use development," said Marilyn Jordan Taylor, a partner with Skidmore, Owings & Merrill.

Residents were not swayed.

"This proposal is too big, too tall, too dense, and will exacerbate traffic," said Seena Parker, the first of 50 East Side residents who spoke against the proposal.

The Planning Commission has until the end of January to act on Solow's proposal. If approved, the project would go to the 51-member City Council.