AMBURG, Germany, Sept. 28 ・In the hours following the Sept. 11 terror attacks, German intelligence agents intercepted a phone conversation between jubilant followers of Osama bin Laden that led the F.B.I. to search frantically for two more teams of suicide hijackers, according to officials in both countries.

The Germans overheard the terrorists refer to "the 30 people traveling for the operation." The Federal Bureau of Investigation already knew that 19 suspected hijackers had died on four planes, and started scouring flight manifests and any other clues for 11 more people still at large, who might have been part of the plot.

One of those may have been Lotfi Raissi, an Algerian pilot brought to court in London today, accused of having acted as the "lead instructor" to 4 of the 19 hijackers while they were all in Arizona. Mr. Raissi, 27, denied any complicity in the terror onslaught.

According to a British prosecutor at an extradition hearing, Mr. Raissi played a crucial background role in the attacks, ensuring that the hijackers had access to pilot training in the United States and monitoring their progress so they were "capable and were trained" for their mission.

The British authorities are investigating whether anyone in their country played a part in the plot to attack America. Scotland Yard has reported that 11 of the 19 accused hijackers passed through Britain earlier this year.

As the authorities across the world try to piece together the conspiracy, the German intercept remains a key clue, a senior American official said, adding that the inquiry is focusing more than ever on Germany and that more F.B.I. agents are being sent here. A top German intelligence official said his investigators were working on the assumption that there were, in fact, 30 people directly involved in the attacks on the World Trade Center and the Pentagon, some outside Germany.

In a 90-minute interview, the German official said the assault had been carried out by a cell of operatives here aided by similar cells in at least three other European countries.

According to other German investigators, another intercepted phone call also offered vital information of a link here. It was between Zacarias Moussaoui, a French-Moroccan arrested in August in Minnesota after strange behavior at a flight school, and a operative in Hamburg who shared an apartment with Mohamed Atta, considered one of the leading hijackers.

That call, dated to Mr. Moussaoui's time in a flight school in Oklahoma earlier this year, is the first substantial evidence linking him to the group that carried out the Sept. 11 attacks.

German investigators have pieced together a diagram of the relationships between the members of what they call the Hamburg cell of Mr. bin Laden's organization, Al Qaeda.

The roughly 20 people in the diagram include Mr. Atta, believed to have been the pilot of the first plane that crashed into the World Trade Center and perhaps the mastermind of the group; Marwan al-Shehhi, who is thought to have piloted the second plane to hit the Trade Center; and Ziad al-Jarrah, suspected of piloting the plane that crashed in Pennsylvania.

In a central spot on the diagram is Ramzi Muhammad Abdullah Bin al- Shibh, who shared an apartment with Mr. Atta, sent money to a Florida flight school seeking to sign up for lessons, and spoke with Mr. Moussaoui some months ago while he was studying flying in Norman, Okla.

German officials have issued an international arrest warrant for Mr. Bin al-Shibh, whose whereabouts are unknown.

The American official explained the decision to increase the F.B.I.'s presence here, saying, "It looks like it was organized in Germany," adding that there is clear evidence of meetings between Mr. Atta, Mr. al- Shehhi and Mr. Jarrah, three of the four suspected pilots.

Mr. Atta has emerged as the central figure partly because of cellphone records obtained by investigators showing him making hundreds of phone calls, including some to other hijackers who then made calls to other people.

The American official said it appeared that some of the hijackers held planning sessions in Hamburg and enrolled in flight training elsewhere in Europe.

The senior German intelligence official said investigators were looking for individuals who had moved in and out of the United States in the weeks and months before the attacks, acting as scouts and logistical coordinators.

Based on a study of previous terrorist operations, particularly the bombings of two American Embassies in Africa in 1998, the official said the scouts would not have been the same individuals as the commandos who carried out the attacks.

"This wasn't done by attackers themselves," the official said of the planning. "It must have been done by certain people who fall through the profiling procedures used by the United States."

The investigators do not yet have concrete evidence that Mr. bin Laden was the author of the attack, the official said. But he said he had no doubt that it was the work of Al Qaeda, because it "has exclusively chosen the United States as a target."

"It has a certain handwriting we can see," he said.

Teams of F.B.I. investigators have been sent to this city and to a German police unit near Bonn, and their number is now being increased.

Today's announcement in England comes a week after Mr. Raissi was arrested under Britain's Terrorism Act. Mr. Raissi was re-arrested under an American warrant today.

When he was seized last Friday, Mr. Raissi was living in Colnbrook, close to London's Heathrow Airport. His wife, Sonia, 25, and brother Mohamed, 29, were also detained but later released. Prosecutors said today that he had been charged in the United States with giving false information when he applied for a pilot's license.

Mr. Raissi qualified as a pilot in 1997 and attended a number of flight schools that were also attended by some of the hijackers in the Sept. 11 attacks, the prosecutor, Arvinda Sambir, said in court today.

"We have sufficient evidence to show not just association with the pilots ・it goes further than that," Ms. Sambir said. "We have evidence of active conspiracy proving correspondence and telecommunications with them as well as video footage of them together. We also have proof they traveled together."

Ms. Sambir said Mr. Raissi visited the United States on several occasions between June and July of this year and on June 23 flew to Las Vegas with his French-born wife Sonia, 25, who works for Air France at Heathrow. From there, he flew to Arizona with a man described as the pilot of the plane that crashed into the Pentagon, identified by American investigators as Hani Hanjour.

"We say he was there to ensure that pilots were capable and trained for this purpose," Ms. Sambir said.

In Arizona, an arrest warrant has been issued for Mr. Raissi, accusing him of making false statements to the Federal Aviation Administration.

Here in Hamburg, investigators are focusing more attention on Mr. Bin al-Shibh, who lived with Mr. Atta and other members of the Hamburg cell at 54 Marienstrasse. The police diagram shows that Mr. Bin al-Shibh transferred 2,000 Deutschmarks, or about $4,200, through Citibank to the West Coast Bank in Florida as a down payment at the same flight school attended by Mr. Jarrah.

Another person whose name is on the diagram is Mamoun Darkazanli, 43, a Syrian businessman with a German wife who worked as a wholesale dealer in office equipment.

Mr. Darkazanli was on the list of 27 individuals and organizations that the Bush administration released last week alleging that they had channeled money to Al Qaeda. American officials said Mr. Darkazanli was an associate of Mr. Bin Laden and took part in a 1996 attack on government troops in Saudi Arabia.

He came to the attention of the German and American authorities in late 1998 as part of the investigation into the African embassy bombings. Mamdouh Mahmud Salim, a Sudanese, whom American officials describe as a right-hand man to Mr. bin Laden, named Mr. Darkazanli during his interrogation by the German police after he was arrested near Munich in 1998. Mr. Salim is currently in jail in New York, awaiting trial on terrorism charges.

When Mr. Salim opened a bank account at the Deutsche Bank in Hamburg, he named Mr. Darkazanli as a co-signer.

According to German investigators, Mr. Darkazanli attended the wedding several years ago of Said Bahaji, a German of Moroccan origin. Mr. Bahaji was in charge of logistics for the Hamburg cell, and last week, the German authorities issued a warrant for his arrest. Eight days before the bombings, he left Germany for Pakistan, German officials have said.

Others at the wedding were Mr. Atta, Mr. Shehhi and Mohamed Heidar Zammar, whose name also appears on the police diagram.