An extensive review of the nation's antiterrorism efforts shows that for years before Sept. 11, ... top leaders never reacted as if they believed the country was as vulnerable as it proved to be that morning. Dozens of interviews with current and former officials demonstrate that even as the threat of terrorism mounted through eight years of the Clinton administration and eight months of President Bush, the government did not marshal its full forces against it. The rising threat of the Islamic jihad movement was first detected by United States investigators after the 1993 bombing of the World Trade Center. The inquiry into that attack revealed a weakness in the immigration system used by one of the terrorists, but that hole was never plugged, and it was exploited by one of the Sept. 11 hijackers. On at least three occasions between 1998 and 2000, the C.I.A. told the White House it had learned where Mr. bin Laden was and where he might soon be. Each time, Mr. Clinton approved the strike. Each time, George Tenet, the director of central intelligence, called the president to say that the information was not reliable enough to be used in an attack, a former senior Clinton administration official said.