"We force them to spend more time and resources on self-preservation. And that distracts them ... from laying the groundwork for the next attack. We keep Al Qaeda off balance."

Still, he said, the border region remained the base of Al Qaeda's leadership, which had developed a more durable structure and a deep reserve of skilled operatives.

"Al Qaeda operating from its safe haven in Pakistan's tribal areas remains the most clear and present danger to the safety of the United States," Hayden said

The United States has been frustrated by Pakistan's inability to eliminate the militants, but Hayden said it deserved credit for a fierce campaign against them in the border area's Bajaur region.

As the war with Al Qaeda continued, veteran enemy fighters were leaving Iraq, where the group was "on the verge of strategic defeat," and heading for Afghanistan, Lebanon, the Arabian Peninsula and North Africa. Others have attempted to plot against the United States.

Al Qaeda has gained strength in North Africa, Somalia and Yemen while suffering deep setbacks in Saudi Arabia and Southeast Asia as well as Iraq, Hayden said.