In what could be a significant setback to rebuilding New Orleans, federal officials said Thursday that it would cost an additional $6 billion to make the levee system strong enough that flood insurance could be issued in the area. That amount would be in addition to the $3.5 billion already being spent to repair the levees damaged by Hurricane Katrina. Without federally issued flood insurance, rebuilding could not proceed in many areas.  The new assessment was disclosed Thursday by Donald E. Powell, the federal coordinator for Gulf Coast rebuilding. The problem evolved in recent weeks when disparate federal agencies began grappling with complex rules and regulations that affect federal flood insurance, the technology of predicting hurricanes and certifications of levee safety standards. [more]