Washington -- Counterterrorism officials said that electronic eavesdropping intercepts obtained in the hours after the attacks on the World Trade Center and the Pentagon indicated that the terrorist operation was carried out by the militant Islamic organization headed by Osama bin Laden.
Intelligence officials said they had collected fresh information after the aircraft crashed into the World Trade Center and the Pentagon. After a briefing session at the Federal Bureau of Investigation, Senator Orrin G. Hatch, a Utah Republican, said that bin Laden associates had been overheard by American intelligence discussing an attack.
"We happened to know just today that we have information that indicates representatives that are affiliated with Osama bin Laden were actually saying over the airwaves, private airwaves that they had hit two targets," Mr. Hatch told reporters.
But one intelligence official said the information was not clear-cut as Senator Hatch had suggested. "It is not definitive, but there certainly are a lot of indicators pointing at bin Laden," he said, referring to the Saudi exile living in Afghanistan who authorities have long identified as the chief architect of anti-American terror.
"There is information developed after the crashes that strongly suggests bin Laden," the official added. "I wouldn't be surprised if there were other, surrogate groups used by his organization as well, since this clearly required large-scale planning."
American officials said that they had no precise warning of the attacks, even this morning as civilian flight controllers apparently tracked the commercial aircraft involved in the attacks as they veered far from their normal flight paths over the northeastern United States.
The officials acknowledged that in recent weeks they had failed to detect any sign of preparations or heightened activity by terror groups that might have signaled that such a large operation was about to be launched - even after a nearly a decade of vastly increased spending to expand the government's ability to thwart terrorism.
One former United States intelligence official said Tuesday that he had been told by current officials that the intelligence agencies had heard after the plane crashes "enough people on the margins of the bin Laden organization going up on their communications saying we did it" to indicate strongly that it was his organization behind the coordinated attacks.
With Mr. bin Laden and his followers in the Al Qaeda organization as the prime suspects, federal authorities opened operational command centers as they began to mobilize manpower for a massive investigation that is likely to expand into a global effort to track down those responsible for the attacks.
But caught by surprise, counterterrorism officials braced for what they anticipated would be a lengthy and unforgiving examination of how they missed the preparations for the attacks, despite an information gathering system designed to prevent catastrophic terrorist acts.
Senator Bob Graham, a Florida Democrat and chairman of the intelligence committee, told reporters that it was "premature" to label the lack of warning as an intelligence failure. But he said that there were "ongoing weaknesses that we need to address in the intelligence community."
Senator Richard Shelby, an Alabama Republican who is vice chairman of the Senate intelligence committee, said the government had received some "general warnings" in the recent past, but he said that there were "no specific warnings," of an assault against the United States.
Mr. Shelby, who said he talked with George Tenet, the director of central intelligence, Tuesday afternoon, said the "C.I.A. hasn't made a definitive ruling," about who is behind the attacks, but said "there are parallels" between today's assault and previous attacks. Mr. Shelby said that the failure to penetrate the plot in advance constitutes "an intelligence failure." If a review determines that there were no hints of the attack in intelligence reporting, "then we got caught flat- footed," Mr. Shelby said. "We have got to be a hell of a lot more aggressive."
While the United States government issued warnings as recently as the Fourth of July holiday that terrorist groups, particularly Al Qaeda, were targeting American interests around the world, those threats had apparently subsided more recently, United States officials said. No warnings ever indicated a serious threat on American soil.
A growing number of officials said the magnitude of today's attacks put them beyond the reach of law enforcement. They said that arrest and trial of conspirators was an inadequate response to what amounted to an assault on the nation's security that could only be dealt with by military force. The re-evaluation of how the United States should respond was apparent in Mr. Graham's remarks. He said that in response to the attacks he would be willing to "reassess" the government's ban on assassinations of foreign leaders.
The attacks left investigators with few clues. The three aircraft that struck their targets were destroyed with all aboard presumed dead, including the terrorists who apparently boarded as passengers.
Attorney General John Ashcroft said tonight that the F.B.I. had established crime scene inquiries in New York, Washington, Boston, Newark and the site of the crash outside of Pittsburgh. He said that thousands of agents were on the case, among them agents stationed in bureau offices abroad and said that those responsible would be brought to justice.
Today, investigators examined radar tapes showing how the four planes took off as scheduled. They flew along customary flight paths, but then two West Coast-bound flights from Boston headed south to New York; a third flight from Dulles to Los Angeles headed west before reversing course to head for the Pentagon.
In addition, federal agents examined the passenger list for terrorists' identities, interviewed security and ground personnel who helped board the flights and sought out security camera tapes for signs of suspicious activities. They hope to recover black boxes on board the planes to review additional data, including cockpit conversations among crew members to learn more details about how the aircraft were commandeered.
According to protocol, investigators awaited rescue and recovery efforts before starting to sift the millions of cubic yards of debris at the two sites to search for evidence like the black boxes of data carried aboard the aircraft. Other investigators are examining evidence at the crash scene outside of Pittsburgh.
Authorities have accused bin Laden and his followers of other terrorist actions against Americans, among them last year's attack on the naval destroyer Cole at the port of Aden in Yemen and the bombing of American embassies in East Africa in 1998. Four men, described as adherents of Mr. bin Laden's movement, were convicted in May of conspiring with him to attack the embassies.
It is unclear what was behind the timing of theterrorist strike today. But the sentencing of Mohamed Rasheed Daoud al-Owhali, one of the men convicted in the East Africa bombings, was originaly scheduled for Wednesday in New York. Next week, M. Salim, a former high-ranking aide to Mr. bin Laden is scheduled to go on trial in New York on charges of stabbing a prison guard while he was awaiting trial on terrorism charges.
The United States has sought to disrupt Osama bin Laden's network for several years, ever since he was identified as a major new force in international terrorism in the mid- 1990's. Following the bombings of the two United States embassies in East Africa in 1998, President Bill Clinton ordered cruise missile strikes on Mr. bin Laden's camps in Afghanistan and on a pharmaceutical plant in the Sudan, which the United States believed at the time to be connected to Mr. bin Laden.
American special forces units have also secretly trained in the past to mount a military operation to capture Mr. bin Laden and destroy his network, and the United States intelligence community has closely tracked Mr. bin Laden's personal movements in Afghanistan in support of potential attacks against him. But fearful of casualties among American soldiers in such a high- risk operation, the White House has never given the go-ahead to the plan.
Today's attacks in New York and Washington bore the characteristics of past attacks linked to Mr. bin Laden's group or their suspected allies in radical Islamic terrorism. It seemed to resemble in some respects a foiled 1995 plot to bomb 12 American jumbo jets.
Ramzi Ahmed Yousef, the alleged mastermind of the first World Trade Center bombing, in 1993, was convicted along with two others of the conspiracy to blow up the passenger airliners over the Pacific. That plot did not, however, include a plan to run the commercial planes into major landmarks in the United States.