The NSA, which eavesdrops on communications worldwide, intercepted messages that said, "tomorrow is zero hour" and "the match begins tomorrow," sources said on condition of anonymity. The intercepted messages gave no details of the time, location or nature of the event that was to take place.
Intelligence agencies aren't sure if the messages were actually a warning of the next day's attacks at the World Trade Center and Pentagon, an intelligence source said Wednesday.
The messages, which were in Arabic, were not translated until Sept. 12, and they have been brought to the attention of the House and Senate intelligence committees that are conducting a joint inquiry into the Sept. 11 attacks.
Vice President Dick Cheney complained to lawmakers Thursday about what the administration is calling inappropriate leak of the intercepts to the press. At President Bush's direction, Cheney called Sen. Bob Graham, D-Fla., chairman of the Senate Intelligence Committee, and Rep. Porter Goss, R-Fla., chairman of the House Intelligence Committee, "to express the president's concerns about this inappropriate disclosure," White House spokesman Ari Fleischer said.
"The information that is being provided to these committees is extraordinarily sensitive," Fleischer said. "The selective, inappropriate leaking of snippets of information risks undermining national security, and it risks undermining the promises made to protect this sensitive information."
There was no immediate comment from Graham and Goss's offices. Their committees are holding a joint inquiry into Sept. 11 attacks.
But Bush has clashed with Congress before over leaks. On Oct. 5, he issued a memo limiting sensitive congressional briefings to the top leaders of the House and Senate and their intelligence committees. He dropped the restrictions a week later after getting assurances from Graham and Goss that they would rein in their members.
Their panel is investigating the events surrounding the attack, problems in counterterrorism efforts and how future attacks can be averted. One U.S. intelligence source said no action could have been taken on the basis of such vague messages.
"Sometimes we get the ambient noise and background chatter. You don't know who is talking," the source said. "Is there actionable intelligence in this? Absolutely not. This is not a smoking gun."
A U.S. official said the two messages were so non-specific that even had they been translated the same day they were intercepted, they would not have rung any alarm bells.
On Wednesday, the congressional panel spent a second day behind closed doors questioning the head of the NSA, Lt. Gen. Michael V. Hayden, as well as CIA Director George J. Tenet and FBI Director Robert Mueller.
Much of the questioning addressed problems that have hindered intelligence-gathering, such as communications problems among agencies, a shortage of linguists and the difficulty of dealing with massive amounts of intercepted communications.
"There were missed opportunities for important information to be brought to the attention of law enforcement," said Sen. Richard Durbin, D-Ill.
Tenet was questioned in detail Tuesday about how the CIA had identified two of the future hijackers at a meeting with an al Qaeda operative in January 2000, but did little to alert U.S. law enforcement agencies.
Yet lawmakers said nothing they've heard so far offered clear evidence that the hijackings could have been prevented.
A U.S. intelligence official, while declining to comment on the NSA intercept, said Wednesday that a piece of raw intelligence that contains only a date provides little useful information.
The official said that both before and after Sept. 11, U.S. intelligence frequently has received threat information that consists of only a date and a vague notion something will happen — and then, nothing happens.
Lawmakers have declined to discuss the intercepts, citing the panel's secrecy. But on Tuesday, Sen. Richard Shelby, R-Ala., the Senate panel's top Republican, said that if certain information collected by the NSA had been translated and disseminated, "perhaps that would have been very useful."
Rep. Silvestre Reyes, D-Texas, said agencies collect "a tremendous amount of data" but using it to stop terrorism is difficult without knowing what kind of an attack is planned.
"Unless we have a clear understanding of a situation like 9/11 coming at us that we can isolate data, it would be pretty impossible," he said.
The intelligence hearings are scheduled to be opened to the public Tuesday, but several lawmakers say that could be postponed. They said the committee and staff need to sift through massive amounts of information and are working with the Justice Department to see what information can be presented in public.
Rep. Ray LaHood, R-Ill., said he doubts public proceedings will begin next week.
"We want to make sure that when we go public that the right people are there and are well prepared, so we don't look like we're flying by the seat of our pants," he said.