London ? British terrorism experts with extensive contacts throughout the Middle East believe many al-Qaida fighters have escaped from Afghanistan and are regrouping in the Middle East, in preparation for more attacks against the United States and its allies.

Because al-Qaida has traditionally let six to 18 months elapse between major attacks, the experts caution, no conclusions should be drawn about the group’s relatively passive stance since the Sept. 11 attacks on the United States.

The analysts generally agree with the Bush administration’s assessment that the threat against the United States remains high, adding that the threat against Europe has been diminished by police raids against a number of “sleeper cells” that were actively planning attacks.

Military and intelligence sources report that a large number of al-Qaida fighters successfully avoided capture in Afghanistan and are making their way home, said Charles Heyman, military editor of the authoritative Jane’s World Armies.

“I don’t believe for one second that al-Qaida has been eliminated by operations in Afghanistan,” he said. “We know they are in Somalia and the Philippines, and we think in Yemen.

“My sources say a vast number of al-Qaida are moving back to Yemen, back to Egypt, back to Saudi Arabia. They say Egypt is a really good place to hide, the teeming masses in the slums outside of Cairo where the roads don’t even have names.”

Heyman estimated that the U.S.-led assault on Afghanistan had reduced al-Qaida’s operational capacity by 15 percent at most. He also said Western leaders have been unwilling to address the underlying causes of the conflict with the Muslim world, meaning that instability will continue for years.