It’s becoming increasingly likely that the future of Ground Zero will be decided by an arbitration panel as a March 11 deadline approaches and the clash between the Port Authority of New York and New Jersey and developer Larry Silverstein shows no signs of abating. Last year, Silverstein had demanded that the Port Authority finance at least two of his planned three towers for the site, but the agency said no. Last month, Silverstein offered to downsize his plans from three towers to two, and pony up an additional $100 to $200 million of his own money to fund the project, but the Port Authority was reportedly unimpressed. And this week, the agency agreed to provide financial support for Silverstein’s first tower and to back the second one after it was one-fifth leased, in exchange for $300 million from Silverstein’s own money — up from the $150 million to $250 million he has already pledged. It was an unwelcome proposal from Silverstein’s perspective, and officials close to the discussion told the New York Times that the two sides are not close to an agreement.