“So far  and I emphasize so far  the score card looks pretty terrible for Al Qaeda,” said Paul R. Pillar, who studied terrorism and the Middle East for nearly three decades at the C.I.A. and is now at Georgetown University. “Democracy is bad news for terrorists. The more peaceful channels people have to express grievances and pursue their goals, the less likely they are to turn to violence.”

If the terrorists network’s leaders hope to seize the moment, they have been slow off the mark. Mr. bin Laden has been silent. His Egyptian deputy, Ayman al-Zawahri, has issued three rambling statements from his presumed hide-out in the Pakistan-Afghanistan border region that seemed oddly out of sync with the news, not noting the ouster of President Hosni Mubarak of Egypt, whose government detained and tortured Mr. Zawahri in the 1980s.

“Knocking off Mubarak has been Zawahri’s goal for more than 20 years, and he was unable to achieve it,” said Brian Fishman, a terrorism expert at the New America Foundation. “Now a nonviolent, nonreligious, pro-democracy movement got rid of him in a matter of weeks. It’s a major problem for Al Qaeda.”

The Arab revolutions, of course, remain very much a work in progress, as the Libyan leader, Col. Muammar el-Qaddafi, orders a bloody defense of Tripoli, and Yemen’s president, Ali Abdullah Saleh, negotiates to cling to power. The breakdown of order could create havens for terrorist cells, at least for a time  a hazard both Colonel Qaddafi and Mr. Saleh have prevented, winning the gratitude of the American government.

“There’s an operational advantage for militants in any place where law enforcement and domestic security are weak and distracted,” said Steven Simon, a fellow at the Council on Foreign Relations and co-author of “The Age of Sacred Terror.” But over all, he said, developments in the Arab countries are a strategic defeat for violent jihadism.