The warnings began shortly after the bombings in Madrid, which came four days before elections there and played a defining role in the defeat of the party of then-Prime Minister Jose Maria Aznar. From the outset, homeland security officials described the threat as targeted at the entire "election process," from the political conventions through Election Day, the electoral college voting and the inauguration.
Still, many in state and local homeland security agencies focused primarily on Election Day, one state homeland security official said. Even between key players such as Ridge and Attorney General John D. Ashcroft, there were sharp differences in interpreting the magnitude of the threat. That was demonstrated by a May news conference during which Ashcroft and FBI Director Robert S. Mueller III took Ridge and others by surprise by warning of the dangers.
Louder alarms were sounded on Aug. 1, when Ridge warned of a high risk of attack based on computer files seized during raids in Pakistan that indicated al Qaeda operatives were casing financial institutions in New York, New Jersey and Washington.
Yet while authorities swiftly went public and raised terror warning levels for the three jurisdictions, analysts behind the scenes soon lessened the significance of the finds. The casing information had been compiled before the 2001 attacks, and other information came only from the Internet. The investigation led to arrests of suspected militants in Britain, but they are now thought to have been targeting London Heathrow Airport rather than U.S. sites.
In addition, a key CIA informer, whose information earlier in the year helped raise the alarms, turned out to be lying, numerous intelligence sources have said.
Analysis of the 2004 threat data continues, with the latest findings sent out by the FBI and the Homeland Security Department as recently as last week. Homeland Security has altered the way it interprets and disseminates "chatter," according to several officials.
"This is the great challenge that DHS faces and the entire national community faces," said Virginia homeland security adviser George W. Foresman. "You have to make some sort of intuitive judgment about information . . . It would be nice to be able to have three or four weeks to do analysis work and make a decision, but we're not in that environment."
Many U.S. security agencies have collectively concluded that the human and political consequences of underreacting are greater than overreacting.
"It's always easier to tighten things up on Day One and then loosen them later, than to have the data and then make a decision to tighten three weeks later," Foresman said. "It's easier to second-guess you then."
Federal intelligence and law enforcement officials describe "chatter" as information from a multitude of sources, including intercepted phone conversations, e-mail exchanges, new and old informers, radio and walkie-talkie transmissions, and tips that come by letter, e-mail and telephone. Much, and perhaps most, of the information turns out to be inconclusive or wrong.
"I wish this was a perfect science where we went into a room, put on our lab coats, figured out an algorithm and then a plan of action," said Assistant FBI Director Michael A. Mason, who heads the Washington field office. "But this is not an exact science. It is not that pat."
Michael E. Rolince, who oversees counterterrorism and counterintelligence in Mason's office, said, "I would not use chatter as the sole indicator by which we raise and lower the threat level. I worry when chatter is high, low or in-between."
Another federal official, who spoke on condition of anonymity, said that a key component of chatter is interviews with prisoners in U.S. military custody at Guantanamo Bay, Cuba, and elsewhere. But that information has gone stale, he said. "The debriefing of prisoners is not giving new information," the official said. "They've been in captivity too long, and the information is old."
D.C. Police Chief Charles H. Ramsey said he is not sure exactly what changed in the intelligence-gathering process since last spring.
"I don't know what specifically changed, but with intel you are constantly trying to verify its credibility as it comes in," Ramsey said. "As time goes on and they have a chance to analyze the information closer, things change."
But Ramsey said that police and federal agents are already doing about as much as they can about security, even without a specific threat to the inauguration.
U.S. Capitol Police Chief Terrance W. Gainer said that with most of central Washington near the Mall and the Capitol closed to vehicles, it would be extremely difficult for a terrorist with a truck bomb to get near the Capitol or the president. But other security measures, including the large number of undercover and uniformed officers, are necessary because of the fear that a suicide bomber could get close to checkpoints.
Staff writers Spencer S. Hsu and John Mintz and researcher Julie Tate contributed to this report.