The City Council and developer Sheldon Solow are locked in last-minute negotiations over the fate of Mr. Solow’s $4 billion mixed-use development project along the East River. The council’s on Zoning and Franchises Committee canceled today’s scheduled vote on the project, and sources close to both sides say that despite recent headway made toward finding a resolution, the two parties are divided on the fundamental issues of height and density in the proposed 6.2 million square-foot plan.

“It’s too big in its present form,” Council Member Tony Avella, who chairs the zoning and franchising committee, said.

If Mr. Avella’s committee doesn’t approve the project by a March 12 deadline, the developer would have to start essentially from scratch trying to make his way through the city’s uniform land use review procedure.

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Mr. Solow’s development calls for the construction just south of the United Nations of six soaring residential towers with about 4,000 apartments, one office tower, and more than 500 public parking spaces.

A number of sources familiar with the negotiations said the height of the buildings, the use of a proposed commercial building, and aspects of the open-space design, which were challenged by the community board 6 and the local council member, Daniel Garodnick, have still not been resolved. Discussions are also ongoing about public passageways from where the Solow property ends to where a proposed waterfront park has been envisioned, according to sources.

A spokesman for Mr. Solow, Michael Gross, declined to comment on details of the negotiations but said, “We hope the City Council will agree that this exciting development will benefit all New Yorkers, adding significantly to the economic and social vitality of the city. Over the past several days, both the City Council and Mr. Solow have worked cooperatively together so that the development can come to fruition.”

The project involves what has been described as the largest stretch of undeveloped, privately owned land in Manhattan. It comes under council review at a time when New York City development projects have suffered a number of recent setbacks caused by a softening economy and the lack of financing caused by the credit crisis. Mr. Garodnick has been mentioned as a possible candidate for council speaker and he has staked out a strong public line against aspects of the proposal.

A senior policy analyst at the New York Municipal Art Society, Jasper Goldman, said the issues of public access are crucial to finding an agreement. “The consensus is that the design is very good, but who will control the space?” he asked. Mr. Goldman likened the current negotiations between the City Council and Mr. Solow to a game of chicken. He said he was optimistic that a deal will be struck.

“Solow has waited a long time for this and the council may feel that they can wait even longer. But everyone wants the plan to pass. It is probably the developer that has more to lose but every one has the chance to win in this. That is the dynamic,” he said.

A series of high-profile projects have been rattled recently by funding setbacks and extended completion dates. The list of projects affected includes the Fulton Street Transit Center, the planned redevelopment of Penn Station and Forest City Ratner’s $4 billion Atlantic Yards project near downtown Brooklyn. Yesterday the New York Times reported that Morgan Stanley would back out of an effort with Tishman Speyer to build a new headquarters at the Hudson Yards Rail Yards on Manhattan’s West Side.

At a press conference yesterday Mayor Bloomberg offered up his assessment of the challenges facing the city, state, and private developers.

“All of these things are going to be difficult to finance in this day and age. And what people don’t understand is the bond markets are saying we have an enormous problem in this country,” he said. “I have no idea whether it is going to get worse or less but it will make financing the city more difficult. It will mean private developers have a more difficult time to do it.”

Mr. Avella predicted that his committee would vote on Mr. Solow’s plan by the March 12 deadline.