We have absolutely no idea how many terrorists are in North America right now. None. The government has admitted that over half of the terrorists who died in the hijackings were ‘new actors’, meaning that they were not identified in any way as terrorists before that day, nor were they on any ‘watch lists’ that any of the intelligence agencies might have.
We do know that Bin Laden has trained somewhere around 50,000 people in his camps. The vast majority of those would have remained in the Middle East. Another percentage of those would be abroad.
So I think we could put an upper limit on the number of terrorists in the U.S. at maybe a couple of thousand, and a lower limit of maybe 50. That’s a pretty wide range of possibilities. Given that officials have already arrested some 350 people, I’d have to guess that the number is closer to 1000 or more.