The Port Authority’s move to liquidate its real estate assets at the World Trade Center site could create stiff competition for developer Larry Silverstein as he tries to fill more than 6 million of square feet of commercial space of his own.

A source involved with the redevelopment effort said that if the Port Authority brokers a deal to sell the development rights to one of its plots to JPMorgan Chase, as is being discussed, the competition for tenants will escalate. That could pit Mr. Silverstein, who is developing three of the buildings at ground zero, against the Port Authority, which owns the trade center site, in a race to sign leases for office space with big-ticket firms such as Merrill Lynch, Lehman Brothers, Morgan Stanley, and others.

When asked yesterday whether he views the Freedom Tower, a Port Authority project, as a competitor for financial service tenants, Mr. Silverstein said he does not. He noted that the building “will serve a different tenancy than will towers 2, 3, and 4,” which he is developing.

Some real estate experts said that even if the Port Authority inks a deal with JPMorgan Chase or another major firm to buy the development rights to the site where the soon to be demolished Deutsche Bank building now stands, south of the trade center footprint, Mr. Silverstein is in a strong position.

“Class A buildings with the capability of hosting large trading floors are very rare commodities,” the president of the Downtown Alliance, Eric Deutsch, said. “So while it may seem there are only a handful of major anchor tenants to go around, there are more than enough to make those buildings a reality.”

The push to find tenants to fill about 9 million square feet of future office space at ground zero comes as Governor Spitzer announced yesterday that he is signing off on plans to build the 1,776-square-foot Freedom Tower, the architectural centerpiece of the site.

Mr. Spitzer’s decision to back the design — which has been mired in delays — is an about-face from his days on the campaign trail less than a year ago, when he called the proposed building a “white elephant.”

Yesterday, he said the strong commercial market in the city and the almost finalized agreement for state and federal agencies to occupy 1 million square feet of the Freedom Tower convinced him the project needed to move forward now. Mr. Spitzer and Governor Corzine of New Jersey both said they were open to selling the tower to a private developer.

“I do not have an opposition at a philosophical level to selling the tower and letting a private entity possibly even undertake the responsibility of building it, leasing it, owning it,” Mr. Spitzer said during an appearance with Mr. Corzine and Mayor Bloomberg in Lower Manhattan.

Mr. Corzine noted that the primary goal of the Port Authority is transportation and that a “strong case” could be made to unload some real estate. Mr. Bloomberg said that if the financial arrangement is a good one for the Port Authority, it makes sense to sell.

The current plan will mean much of the commercial office space will hit the market in Lower Manhattan around the same time, in 2012. Some have said too much space could take years to fill, as it did with the original World Trade Center. But those involved are banking on the hot commercial market.

A source familiar with the redevelopment said JPMorgan Chase probably approached the Port Authority about the site, figuring it could get a better deal than it would by negotiating with a private-sector developer.

A spokesman for the Port Authority, Stephen Sigmund, said it was not useful to speculate on “who might drive a harder bargain.” He also said the Port Authority believes that building the entire site simultaneously would allow Mr. Silverstein and the Port to benefit from a critical mass effect.

“It means the buildings become attractive at once, the whole site becomes attractive at once,” he said.

Mr. Spitzer left open the possibility for negotiations on how to arrange victims’ names on the World Trade Center memorial. In a move that has angered some families, Mr. Bloomberg has said names will be grouped by employer but will not include ages or company names.

“It is something that we will try to work through at the right time and the right place and get to a resolution that satisfies everybody,” Mr. Spitzer said.