Deadline for Ground Zero Plan Nears
March 30 deadline set by New York Gov George E Pataki approaches concerning settlement of differences between developer Larry A Silverstein and Port Authority of New York and New Jersey over rebuilding of World Trade Center site; authority wants Silverstein to build Freedom Tower and relinquish control of major portion of site so work can proceed more quickly; financial analysis shows Silverstein could exhaust his money for project, default on lease in 2009 and still walk away with half a billion dollars (M)