The World Trade Center rebuilding effort sank into confusion this week, as the projects top supervisor resigned while designers scrambled to address mounting security concerns. The main issue is the projects centerpiece, the 1,776-foot Freedom Tower. New York police warned last month that the tower would be too close to the street, leaving it vulnerable to a terrorists truck bomb. Architects are now assessing whether the tower could be placed elsewhere on the 16-acre site. But such a major change could push back the planned 2009 opening by a year. We are going to do this right, said Mayor Michael Bloomberg, and its not easy.