Uncertainty is building around Governor Pataki’s promise to fill about 30 floors of the Freedom Tower with government tenants, a requirement to hold together the April deal between the state, the Port Authority, the city, and developer Larry Silverstein for developing ground zero.

The chairman of the Port Authority, Anthony Coscia, at a breakfast yesterday sponsored by Crain’s New York Business, said the Port Authority could “rethink” the Freedom Tower if the state does not secure the Freedom Tower leases by September, as planned. Although blasting was performed this week in preparation for the construction of the Freedom Tower, a Port Authority official told the New York Observer that changes might involve shrinking the tower from its proposed height of 1,776 feet.

“The agreement contemplates that we will go between now and September and we will decide whether or not we have the kind of leases for that building which make it a financially viable project,” Mr. Coscia said.

The chairman of the Port Authority added that he was “optimistic” that the state could secure the leases by the deadline.

In the final days of bitter negotiations between Mr. Silverstein, and officials from the Port Authority, the state, and the city, the developer held back from signing a deal – largely, he said, out of fear that the government would fail to live up to its promises. One of the deal’s most tenuous contingencies was the state’s agreement to secure Freedom Tower lease commitments by government tenants at market rates.

Mr. Pataki said yesterday in a telephone interview that the Freedom Tower “is designed, is under construction,” and would be both a symbol of resurgence and “something that is economically viable.”

A spokeswoman for Mr. Pataki, Joanna Rose, said the state has had “extremely productive” discussions with government agencies regarding moving into the Freedom Tower, and she said the governor’s office remains “confident” that the September goal will be met. Press reports have named the U.S. Customs Service and Border Protection, the Secret Service, and the FBI as possible tenants, but no agreements have been signed.

While Mr. Pataki has championed the Freedom Tower in part because of its symbolic value, others consider it to be the commercial white elephant of the site. The tower would be located far from transportation and stand out as a plausible terrorist target. Mr. Coscia said yesterday that there was “a substantial amount of apprehension” among Port Authority employees about working in the Freedom Tower.

The city and the Port Authority, which owns the 16-acre former site of the World Trade Center, have each agreed to take 600,000 square feet of space in another tower planned along Church Street. Silverstein Properties declined to comment yesterday.

A Manhattan Institute fellow who specializes in municipal finance, Nicole Gelinas, said development plans at ground zero are far from a “done deal” and that Mr. Coscia’s comments add more uncertainty. “They haven’t solved the main problem: that the Freedom Tower seems like it is not financially viable. The design was done for political reasons, not commercial reasons,” Ms. Gelinas said.

She said that if the Port Authority opted to shrink the Freedom Tower, it would be a further reduction of the bistate agency’s risk in the ground zero redevelopment plan.