PARIS — Osama bin Laden's Al Qaeda network is in headlong retreat in Afghanistan and European police are rounding up other suspected terrorists, but investigators say a web of Islamic extremists remains on the continent and still poses a threat of attacks.
European authorities believe that triumphs on the battlefields in Afghanistan, including the killing of Al Qaeda military commander Mohammed Atef, and their own quieter victories in cracking terror cells have disrupted Bin Laden's network.
But the loose-knit organization already in place does not need direct orders from the top to function. "Sleeper" terrorists in position before Sept. 11 could be planning attacks against Western interests in general and U.S. targets in particular, authorities say. A pan-Islamic legion of thousands has trained in the now-devastated Al Qaeda camps in Afghanistan and operates underground throughout Europe, according to police and terrorism experts.
"They have succeeded in creating a very motivated core that is present everywhere," said Alain Grignard, a Belgian expert on Islamic terrorism who is also a police commander in Brussels. "They don't work like an army with a general who tells them what to do. The groups have a certain autonomy."
New arrests in Spain and France have contributed to a picture of an interconnected network of cells that reaches into Britain, Italy, Belgium, Germany and the Netherlands.
On Sunday, a Spanish judge accused members of an alleged terror cell in Madrid of providing false identity cards and money to some of the Sept. 11 hijackers.
The eight suspected cell members, arrested last week, were "directly related to the preparation and development of the attacks perpetrated by suicide pilots on Sept. 11," Judge Baltasar Garzon wrote in a court order.
In charging the Islamic militants with membership in Al Qaeda, prosecutors cited telephone intercepts and phone numbers found in the papers of one of the suspected hijackers, Spanish newspapers reported. If proved, the charges would provide fertile new ground for U.S. authorities in the Sept. 11 investigation.
European authorities fear that other extremists with loose ties to Al Qaeda may attempt attacks, either because they already had operations planned or because they want to make a statement in the wake of Al Qaeda's military losses. And individuals might spontaneously strike against "targets of opportunity."
Europe is central to the U.S.-led coalition against terrorism because the Sept. 11 attacks on the United States were carried out by terrorists who either lived in Europe or passed through European capitals in the months before the hijackings.
The investigation of the hijacking plot has focused increasingly on evidence of links between some of the hijackers and accused Islamic terrorists in Europe, especially because U.S. authorities apparently have failed to implicate any of the roughly 1,200 suspects detained in the U.S. in the Sept. 11 attacks.
The ultimate fear of investigators in Europe is that an already entrenched team of the caliber of the Sept. 11 hijackers is preparing a devastating attack or series of strikes.
A report issued Wednesday by the British government warned: "Based on our experience of the way the network has operated in the past, other cells, like those that carried out the terrorist attacks on 11 September, must be assumed to exist."
There are indications that "two or three" major plots were set in motion before the hijack attacks in the United States and that they could be well underway, a European intelligence source said.
"I think the Al Qaeda operations are in a real advanced stage of planning," the intelligence source said. "Osama bin Laden follows a plan along a certain timeline, going step by step, and the next step was planned long ago."
Al Qaeda has clearly been weakened by the combined military and law enforcement assault around the world. But because they are often self-contained and plan well ahead, Al Qaeda cells remain a viable threat, a U.S. official said.
"If their operation is already in place and they've already done their intelligence and surveillance, they could still pull something off," the official said. "You can't rule out the most obscure, far-fetched Tom Clancy scenario."
Another sobering assessment came from a well-placed observer: Sheik Omar Bakri Mohammed, a legal scholar in London who denies allegations that he recruits militants for training in Afghanistan. Bakri insists there is no proof that Bin Laden ordered the Sept. 11 attacks, but he added: "If he did, he is capable of doing anything in Europe."
European police keep finding evidence of the breadth of the Bin Laden organization.
In Madrid, Spanish police said the alleged kingpin of the cell broken up last week had direct contact with Bin Laden. It was the first arrest of such a potentially prominent figure since the crackdown began.