But experts say the likely truth is the opposite: Only the Sept. 11 attacks allowed the analysts to find and make sense of the messages, which NSA translated Sept. 12.
That's because the torrent of communications that pours into NSA's global eavesdropping network is far too great to translate and analyze - even if the agency were not suffering from a severe shortage of qualified linguists.
"The Information Age has overwhelmed us," said former New Hampshire Sen. Warren B. Rudman, former chairman of the Senate intelligence committee and the President's Foreign Intelligence Advisory Board. If NSA was unable to warn of the attacks, it's "not for lack of trying," Rudman said.
Even when messages sent within the al-Qaida terrorist network are snagged and read in timely fashion, their deliberately ambiguous wording makes them tough to interpret, intelligence experts said. The Sept. 10 messages - "the match begins tomorrow" and "tomorrow is zero [hour]" - are typical of the sort that bedevil NSA analysts.
"It puts the intelligence analyst in the impossible situation of telling a real threat from some guy talking nonsense in a cafe in Kandahar," said Matthew M. Aid, an intelligence historian writing a book on NSA. Depending on the context, the messages might as easily have referred to a soccer match or a long-awaited birth as to an act of terror, he said.
Citing security concerns, Vice President Dick Cheney complained yesterday to lawmakers about the leak of the intercepts, which were discussed in closed committee hearings on the intelligence agencies' conduct before Sept. 11.
At President Bush's direction, Cheney called Sen. Bob Graham, chairman of the Senate Intelligence Committee, and Rep. Porter J. Goss, chairman of the House Intelligence Committee, "to express the president's concerns about this inappropriate disclosure," said White House spokesman Ari Fleischer.
Fleischer called the leak "alarmingly specific."
"The information that is being provided to these committees is extraordinarily sensitive," Fleischer said. "Public disclosure of that information can damage our ability to protect the country. So the president does feel very strongly about it."
In response, Graham and Goss asked Attorney General John Ashcroft to investigate the leak of classified information.
"We are entrusted to keep secrets, so when I hear there is a leak that may have come from our committees, it's a matter of great concern," said Goss, a Florida Republican and former CIA officer.
Fleischer said a 1998 leak revealing that U.S. intelligence agencies were intercepting Osama bin Laden's satellite phone conversations led the Saudi terrorist to stop using that phone. If terrorists learn of U.S. eavesdropping capabilities, "they're going to change their methods," he said.
In recent years, however, the government has done little to hide the fact that it eavesdrops on known terrorists.
Last year, federal prosecutors in the trial of four men charged in the bombing of U.S. embassies in East Africa repeatedly cited NSA and FBI eavesdropping on the plotters. The intercepted messages were critical to convicting the men - but they had been too vague to stop the attacks in the first place.
The intelligence committees' inquiry wrapped up the third week of closed-door hearings Wednesday. The appearance this week of NSA's director, Lt. Gen. Michael V. Hayden, led to the first official scrutiny of the eavesdropping agency's work prior to Sept. 11.
With more than 20,000 people at the main campus off the Baltimore-Washington Parkway and several thousand more at listening posts around the world, NSA is the nation's largest spy agency. Graham said this week that it produces about 75 percent of all the intelligence collected by the government.
But until now, the agency had escaped the kind of criticism prompted by the FBI's failure to act on agents' concerns about suspicious foreigners enrolled in flight schools and the CIA's failure to follow up on the arrival in the United States of two of the Sept. 11 hijackers.
Yesterday, no experts were willing to conclude that NSA's Sept. 10 intercepts represented the same degree of failure. Though the Arabic-language messages originated in Afghanistan, nothing is publicly known about who the speakers were.
"It seems to me to be much ado about not very much," said Loch K. Johnson, an intelligence expert at the University of Georgia. "Translating this stuff in two days is really not too shabby."
Jeffrey T. Richelson, an authority on U.S. intelligence and researcher at the National Security Archive in Washington, agreed.
"From everything I've seen, it seems to me that far more of the problem lies with the FBI, where there was some kind of concrete information" about flight schools, he said.
Steven Aftergood, intelligence policy analyst at the Federation of American Scientists, said the intercepts actually suggest NSA is managing to track terrorists despite the challenges posed by the global communications explosion.
"To tell the truth, I was impressed that they were able to identify these particular messages out of the daily avalanche of traffic," Aftergood said. "What this tells me is that they still have something going for them. This is not a totally obsolescent agency."
Former NSA employees said yesterday that the agency monitors a large and constantly changing list of telephone numbers and e-mail addresses used by al-Qaida operatives. Each item on the watch list is given a priority ranking, based on whether it has been used by leaders of the terror network or lesser figures.
Conversations on the targeted telephones, picked up by NSA's fleet of eavesdropping satellites, are automatically recorded and sent to the computer terminals of relevant translators and analysts.
But finding the right phone numbers and computers is a daunting task in an era of ballooning communications. There are about 800 million cell phones in use worldwide, and about 500 million people have e-mail access on the Internet, according to industry estimates.
The NSA's charter "is to collect and cast the widest possible net on the widest variety of communications, and that can literally be millions of data points at any given time," said Anil Phull, a former NSA official now at the Yankee Group, a technology research firm in Boston. "And so to find that top 1 percent of 1 percent of relevant information that needs to be further analyzed and acted upon - that's a classic needle in the haystack problem."
NSA's counter-terrorist efforts also are crippled by a severe shortage of linguists. The agency's Web site advertises openings for speakers of Dari, Arabic, Urdu, Swahili and Greek, among other languages.
Near-native fluency is often required to understand the nuances of a fuzzy phone intercept, said Aid, the intelligence historian who is a former Defense Department linguist.
"The quality of the recording can be very poor. There can be slang or code words used," Aid said. "It can take four hours to translate a five-minute conversation."
For the government to take action on the basis of an intercept, the message and analysis must be passed on to NSA's "customers" at the Pentagon, the White House, the CIA and the FBI. But those recipients of NSA intelligence sometimes complain if they are given every intercept that could conceivably warn of an attack.
"NSA has often been accused of crying wolf," Aid said.
In 1999, for instance, NSA intercepts warned that bin Laden might be plotting an attack on U.S. targets in Europe, possibly Albania. Planned trips there by Secretary of State Madeleine K. Albright and Defense Secretary William S. Cohen were canceled, but no attacks occurred.
Staff writer Tom Bowman contributed to this article.