ASHINGTON, Sept. 24 — Two weeks after the terrorist attacks in New York and on the Pentagon, investigators have not yet identified any knowing accomplices in the United States or uncovered a broad support network that assisted the 19 hijackers, a senior law enforcement official said today.

The official, who is actively involved in the investigation, said that a key to unraveling the plot might lie in Germany, not the United States, and that a team of agents had been dispatched to pursue leads there.

Based on investigators' portraits of the suspected hijackers and their movements before the Sept. 11 attacks, the official said, federal agents are investigating whether the plot had its origins in Germany and then branched out to hubs in Newark, Boston, Florida and Maryland.

While some reports have suggested that there were other terrorist cells in the United States and even failed plots to hijack other airplanes on Sept. 11, the official said the arrests of hundreds of people and interviews with thousands of others had produced little hard evidence to support either suspicion.

"Thus far we cannot connect any of those people that we're looking at to any of those 19" hijackers, the official said.

Investigators have evidence that some people unwittingly assisted the hijackers but did not know about the overall plan. They are still pursuing leads in the United States that other people may be tied more closely to the hijackers and the plot.

Attorney General John Ashcroft said today that 352 people had been arrested or detained and that an additional 392 people were being sought for questioning.

If this new theory of the case proves true, it will have the effect of assuring the public that no conspirators remain hidden in the United States at a time when the White House is planning military reprisals.

While not ruling out future discoveries, the authorities are saying that to date they have not found evidence of organized groups linked to Osama bin Laden's terrorist organization, Al Qaeda, still operating in the United States, or any direct evidence that the 19 men identified as the hijackers who crashed airliners into the World Trade Center and the Pentagon were associated with other groups planning future attacks.

Officials said that promising information had been developed in Germany, where the police seek two men who they believe may have been directly involved in the plot.

One suspected hijacker, Mohamed Atta, believed to have played a central role in coordinating the plots, lived in Hamburg while studying engineering. He was killed aboard the American Airlines flight that struck the World Trade Center's North Tower.

Some investigators still believe that the plot was so intricately timed that it almost certainly required help from accomplices on the ground who helped scout airlines, airports and flight training schools.

But as days pass without evidence of their presence, other investigators suggest that the hijackers designed their plot to self-destruct, leaving behind no trace of other conspirators or much documentary evidence.

Moreover, investigators have still not identified a chief architect of the plot who might have headed a decision-making structure and then fled.

A senior law enforcement official said that 17 of the 19 hijackers were not known to intelligence or law enforcement officials before the Sept. 11 attacks. Two of the hijackers, Khalid al-Midhar and Nawaf alhamzi, were placed on the government's official watch list for suspected terrorists before the attacks.

Saying that thousands of people had been trained at Mr. bin Laden's camps in Afghanistan, this official acknowledged that Western intelligence could not track them all.

"It shouldn't surprise us that they have people that don't come up on anybody's radar screen, in our country or elsewhere, who can legitimately come here, travel on a legitimate visa, pay bills, stay out of trouble, take training and launch an attack like this," the official said. "It's staggering in its complexity and the discipline is very impressive."

The official said investigators had collected electronic intercepts connecting the attacks to Al Qaeda. But the official said that evidence would probably not be made public in the government's "white paper" that is to connect Mr. bin Laden to the attacks.

The official said the authorities were still sifting through thousands of bank records to determine whether the hijackers received financial support from Al Qaeda.

Investigators are pursuing other avenues in the United States. Today, one man was charged in Northern Virginia with helping three of the suspected hijackers fraudulently obtain Virginia driver's licenses last month; a second man who aided with the licenses is cooperating and was not charged, prosecutors said. But officials said they did not believe that either man had any knowledge of the hijacking plot.

The F.B.I. searched an apartment in Paterson, N.J., last week and showed neighbors photos of two of the hijackers on the flight from Newark that crashed in Pennsylvania, residents said today.

Jamie Diaz, who also lived in the building, at 486 Union Ave., said today that one man had lived there about six months, and that they both moved out about a week before the hijacking.

Officials said that reports that other hijacking teams were prepared to commandeer other flights on Sept. 11 remained only a theory, even though searches of planes turned up boxcutters similar to those believed to have been used by the hijackers.

Last week, Mr. Ashcroft said other planes might have been at risk on Sept. 11. But reports of other hijackers who may have boarded or tried to board other flights appear to lack credibility, the officials said.

Law enforcement officials in recent days said the hijackers planned for the attacks by monitoring the airports, and even taking the cross- country flights, more than once. "I'm starting to believe only two weeks into this that they did this with only a minimal amount of support in the U.S.," one official said.

The investigation has also spawned a secondary intelligence inquiry of huge proportions intended to glean fresh threats in the United States and overseas.

A senior law enforcement official said some investigators had theorized that the hijackers were able to keep the plan secret by letting only one member of each team know that the planes would be crashed into buildings. The others, the official said, might have believed that the jets would be landed at an airport where demands would be made.