More delays are in the works at the long-stalled World Trade Center site.

Developer Larry Silverstein on Tuesday said an impasse with the Port Authority of New York and New Jersey has him turning to binding arbitration, which could add months onto rebuilding timetables.

Silverstein blamed the agency's "inability to meet its rebuilding obligations," which he claims is hampering his ability to lease space at three office towers on the 16-acre site.

"One way or another, we must resolve, once and for all, the disputes that have arisen as a result of the Port Authority's continued and admitted delays," said the developer in a statement.

A spokesman for Silverstein said the company is still waiting for a fair proposal from the agency that guarantees over $3 billion in financing for the two towers.

But the Port Authority, which has paid $100 million in penalties for not meeting deadlines, said Silverstein has been unwilling to modify his development to reflect the economic downturn.

The agency's Executive Director Chris Ward said in a statement, "The bottom line is Silverstein didn't miss the market, the market missed Silverstein."

Governor David Paterson sent a letter to Silverstein Monday directing the Port Authority to draft blueprints without including Silverstein's buildings.

A Port Authority spokesman said a meeting Wednesday at Paterson's request has been called off and that the agency did not respond to Silverstein's new call for arbitration.

Paterson also called Silverstein's move "disappointing" but called for both sides to continue negotiations.

Yet the developer does have powerful allies in the city.

In a statement, Mayor Michael Bloomberg called the latest developments, “unacceptable” and demanded greater oversight of the Port Authority’s progress at the site.

State Assembly Speaker Sheldon Silver also backs Silverstein's plans.

"Right now, we're at a stalemate. So it can't be more delays than no plan for the future, which is basically what the Port Authority has set up here," said Silver.

The speaker, who also previously refrained from criticizing the governor, criticized the way Paterson is handling the situation.

"I think what happened here is while the governor said, 'Let's sit down and talk,' what's he's basically said in his message is the Port Authority is right, and that's the thing that's unacceptable about what he said," said Silver.

This impasse came as the Daily News reported that a study by the Lower Manhattan Construction Command Center finds every project at the site is further behind schedule than originally thought.

The report puts the completion date of the Freedom Tower in 2018 and the September 11th Memorial in 2013, despite the push to have a memorial at the site by the 10th anniversary of the attack.

The LMCCC says the analysis is a preliminary draft for discussion purposes only and that the dates should not be considered valid until the ongoing review process is completed.

Port Authority officials disputed the predictions.