ASHINGTON, Sept. 13 — Attorney General John Ashcroft said the federal authorities had identified 18 men who hijacked the commercial jets used in Tuesday's terror attacks, while investigators accelerated a nationwide manhunt for dozens of accomplices believed to have supported the assaults on the World Trade Center and the Pentagon.

One man identified by federal officials was Mohammed Atta, who they said had lived in Germany, trained as a pilot in Florida, arrived from Maine as a passenger at Logan Airport, and boarded American Airlines flight 11 bound for Los Angeles. That plane, the first to be hijacked, flew into the World Trade Center at 8:45 a.m.

The 18 men were all ticketed passengers on the four planes involved in the terror operation, including two that struck the World Trade Center towers, one that hit the Pentagon, and another that crashed in rural Pennsylvania, according to F.B.I. Director Robert S. Mueller III. The authorities have not released a complete list of the names and nationalities of the hijackers.

One associate of the hijackers is said to have surrendered to federal authorities in Florida and is cooperating with law enforcement officials. Other accomplices remain at large and most are believed to be in the United States, although their whereabouts are unknown, law enforcement officials said. The widening number of suspects sought by investigators reflects what counterterrorism officials said was a highly organized and complex plot.

Chastened by their failure to predict the attacks, United States officials have begun the task of sifting back through previous intelligence reports to determine whether they missed any indications that an assault was imminent. Officials said that in hindsight, some strands of intelligence now appear far more significant than they did at the time they were collected.

Intelligence officials believe the attacks were organized by Osama bin Laden, the Saudi exile who has been implicated in a series of bloody assaults against Americans.

Officials pointed in particular to an intelligence report before Tuesday's attacks that at least one member of Mr. bin Laden's family had been told to leave Saudi Arabia and get to a safer location — possibly Afghanistan — before an impending deadline.

"There was a reference that a member of bin Laden's family should remember to get here before the work is done," said one United States official familiar with the intelligence. "That only sticks out in hindsight."

Officials also said that in August, the Central Intelligence Agency issued a secret report warning senior policy makers that Al Qaeda hoped to launch a strike against the domestic United States.

The report combined both new and older intelligence gathered by the C.I.A. and other American intelligence agencies to depict Mr. bin Laden's long-term desire to shift from attacks on American interests overseas to targets in the United States itself.

But the report, included in a classified publication distributed to top government officials known as the Senior Executive Intelligence Brief, did not provide any detailed warnings related to Tuesday's attacks on the World Trade Center and the Pentagon, officials stressed. And, officials stressed, it was largely a reiteration of previous warnings from the C.I.A. that Mr. bin Laden was eager to launch domestic attacks. Meanwhile, investigators examining records at flight training schools in Florida and elsewhere have determined that other people who may have links to the terror plot but who did not take part in Tuesday's attacks received flying lessons at the schools, law enforcement officials said.

They said that the discovery of additional pilots who might form the nucleus of additional hijack teams has heightened security concerns. The whereabouts of the other pilots is unknown, the officials said.

The pilots arrived from Middle Eastern countries and enrolled in the schools a year or more ago, in some cases at the same time as pilots already tied to the terror plot. Some appeared to be friends of the pilots and trained with them.

Investigators are reviewing whether any of these pilots were booked on flights on Tuesday.

The C.I.A.'s warning to top officials in August about Mr. bin Laden's intentions followed earlier warnings by the C.I.A. in June and July of potential terrorist attacks against American interests that officials thought were to be timed to the Fourth of July holiday, officials said.

The officials said that the August report was designed, in part, to remind senior policy makers at the White House, State Department and Pentagon that even though no strike had occurred over the July Fourth holiday, Mr. bin Laden still seemed intent on launching an attack, possibly inside the United States. United States officials stressed that the C.I.A. had issued similar warnings of a domestic attack several times over the past few years.

The officials added that that United States intelligence had long known of Mr. bin Laden's desire to bring his terror campaign to Americans at home, rather than through attacks on embassies and other American sites abroad.

The fact that the report was published inside the government last month did not indicate that the C.I.A. had any specific information about a pending attack inside the United States, officials emphasized. In fact, American intelligence officials have acknowledged since the attacks that they had no specific warnings that could have led them to predict Tuesday's attacks.

United States officials also said that two — and possibly three — of the 18 hijackers were on the government's watch list designed to prevent their entry into the country. But they appear to have entered the United States before they were added to the list.

Officials added that a review of the 18 hijackers shows that some of them had entered the country several times on valid passports and visas. Flight manifests show that the hijackers were sitting in rows together near the front of each aircraft, one United States official said. At least some appear to be related, with the same family names.

In Portland, Me., officials said that a videotape taken at the airport shows two men passing through security gates at 5:53 a.m. the day of the attack, headed for a Boston flight. Officials identified the men as Mr. Atta and Abdul Alomari. Both men made the connection onto American Airlines Flight 11, one of the flights that later struck the World Trade Center.

Officials in Boston said that tapes of the garage at Logan Airport show that a car believed to have been used by the hijackers drove through the parking area at least four times in the week before the attack.

At the same time, the investigation broadened to other states. One per son was arrested in Fort Smith, Ark., in connection with the investigation. Hady Hassan Omar, 22, was taken in handcuffs out of the F.B.I. office at Waldron Place in Fort Smith by law enforcement officers. A worker at the detention center said Mr. Omar was being held for the Immigration and Naturalization Service. Information on charges was not immediately available.

In New Jersey, where officials believe that the hijackers received assistance from accomplice, Sherri Evanina, a spokeswoman for the F.B.I. in Newark, said that five men were detained late Tuesday after the van in which they were driving was stopped on Route 3 in East Rutherford.

She said witnesses had reported seeing the men celebrating the attack on the World Trade Center earlier in the day in Union City. "They were seen leaving the location after they were celebrating," Agent Evanina said. "They were watching the entire event from their location."

Angry witnesses reported the men's license plate to the authorities. The plate was registered to Urban Moving Systems, a truck-rental company based in Weehawken, N.J., Ms. Evanina said.

The five men were detained on administrative grounds by the Immigration and Naturalization Service, officials said. No criminal charges have been filed against them.

Dominik Suter, the owner of Urban Moving Systems, did not return several telephone messages left at his office. A woman who answered the telephone at the company's offices, but would not give her name, said, "We have no comment." She would not give her name."

Kerry Gill, a spokesman for the Immigration and Naturalization Service in Newark, said the F.B.I. turned over the individuals to I.N.S. on Wednesday. He said "they appeared to be Israeli citizens and all five appear to be removable from the United States."

Mr. Gill said the men could be deported because all "were determined to be either out of status or to have violated his or her non-immigrant status," meaning that they had outstayed the length of their visas or had violated specific terms of their visas.

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