Counterterrorism and nuclear experts told the Post they considered the danger more distant than immediate, pointing to enormous technical and logistical obstacles confronting would-be nuclear terrorists, and to the fact that neither al-Qaida nor any other group has come close to demonstrating the means to overcome the snags.

"I would say that from the perspective of terrorism, the overwhelming bulk of the evidence we have is that their efforts are focused on biological and chemical" weapons, said John R. Bolton, undersecretary of state for arms control and international security. "Not to say there aren't any dealings with radiological materials, but the technology for bio and chem is comparatively so much easier that that's where their efforts are concentrating."

But despite the hurdles, the danger that bin Laden will get a nuke cannot be dismissed. "The thing to keep in mind is that while it is extremely difficult, we have highly motivated and intelligent people who would like to do it," said Daniel Benjamin, a former National Security Council staff member and senior fellow at the Center for Strategic and International Studies.

Even if bin Laden could succeed in obtaining nuclear material, there remain a great many steps between that and setting off an explosion, according to the Post.

Experts told the daily that the uranium would have to be smuggled out of the facility where it was kept and then transferred, possibly across several borders, seaports and airports, to a location where the nuclear device could be assembled.

Intelligence sources say bin Ladan would prefer to get a nuclear weapon that's already assembled, probably by stealing or buying one now in the the hands of the Russians or Pakistanis. Even then, experts told the Post, it would be very difficult for terrorists to figure out how to work a Russian or Pakistani bomb.

Editor's note: