decade after al-Qaeda issued a global declaration of war against America, U.S. spy agencies have had little luck recruiting well-placed informants and are finding the upper reaches of the network tougher to penetrate than the Kremlin during the Cold War, according to U.S. and European intelligence officials.

Some counterterrorism officials say their agencies missed early opportunities to attack the network from within. Relying on Cold War tactics such as cash rewards for tips failed to take into account the religious motivations of Islamist radicals and produced few results.

Since the attacks of Sept. 11, 2001, officials said, al-Qaeda has tightened its internal security at the top, placing an even greater emphasis on personal and tribal loyalties to determine who can gain access to its leaders.

Alain Chouet, former chief of the security intelligence service of the DGSE, France's foreign spy agency, said it can take years for informants to burrow their way into radical Islamist networks. Even if they're successful at first, he said, new al-Qaeda members are often "highly disposable" -- prime candidates for suicide missions.

He said it might be too late for Western intelligence agencies, having missed earlier chances, to redouble efforts to infiltrate the network. "I think you cannot penetrate such a movement now," he said.