AFTER years of false starts and broken promises, we have reached a defining moment in the rebuilding of the World Trade Center. By Friday, the Port Authority of New York and New Jersey and the site's developer, Larry Silverstein, must make a choice: Will they broker a compromise that allows them to move forward with rebuilding the historic heart of our city? Or will they allow their dispute to return to arbitration, condemning the World Trade Center site to years more of delays? For the two of us, the choice is clear. In the days after the city was attacked, New Yorkers vowed to rebuild, to make Lower Manhattan whole again. And with new schools, parks and housing, it has been rejuvenated as a dynamic, bustling community. There has also been some important progress at ground zero. The memorial is on track to open in time for the 10th anniversary of the attacks, next year. The tower at 7 World Trade Center is a commercial and critical success. Construction of the Port Authority's 1 World Trade Center, Mr. Silverstein's 4 World Trade Center and the Metropolitan Transportation Authority's Fulton Street Transit Center is well under way. But the latest stalemate between the Port Authority and the developer, which has been dragging on since last summer, now threatens to overshadow and overwhelm all of the progress. At the root of their dispute is financing for the office towers that are to be built along Church Street, on the east side of the complex. With capital markets still tight, Mr. Silverstein is seeking credit assistance from the Port Authority for two of his skyscrapers; but the Port Authority is willing to fully back only one of them. Because the new World Trade Center has been designed so that all the buildings share key infrastructure, an indefinite delay for one building would delay the entire eastern side of the site. That would mean the loss of 10,000 construction jobs and leave us with an enormous empty lot where we should have a revitalized Trade Center. That outcome is unacceptable. And it doesn't have to end up this way: Mr. Silverstein and the Port Authority have one day to hash out an agreement that fulfills their moral obligation to our city. Several months ago, the two of us spelled out a compromise. It's a deal that's still within reach. Our proposal would require Mr. Silverstein to invest significantly more equity and take on more risk, and the Port Authority to provide more temporary credit assistance to move construction forward on both towers. Mr. Silverstein has been receptive to this plan, but the Port Authority has not, couching its opposition as an effort to protect taxpayers and preserve its ability to pay for other transportation and development projects in the region. Its continued intransigence, however, comes with its own price. Delays at the site have already cost the Port Authority tens of millions of public dollars. Not only would further delays cost much more, but rent proceeds from a thriving World Trade Center would provide money for the Port Authority's other transportation projects around the city, including Moynihan Station and a new passenger rail tunnel under the Hudson River. From the beginning, the redevelopment process was always intended to be a public-private collaboration. We need a reinvigoration of that partnership now more than ever. The parties have one day to produce a realistic schedule, a budget and a financing plan for the World Trade Center. The future of Lower Manhattan — and a piece of our national pride — depend on it. – New York Times Michael R. Bloomberg is the mayor of New York. Sheldon Silver is the speaker of the New York State Assembly. __