To me the key to this argument is "reasonable suspicion". In principle, I agree with the idea that if a person is a threat to the security of our nation then all means necessary should be enacted to ensure our domestic safety. The sticking point is "reasonable".
Many times throughout history "reasonable" suspicion was used to curtail the freedoms of innocent people. During the time before the American Revolution, the British used writs of assistance in an effort to stop smuggling. These were unspecific, undated documents that turned into de facto blank search warrants. The abuses of British customs officials through these writs laid the foundation for the inclusion of the fourth amendment to the US Constitution.
I fear the suspension of attorney/client privilege could turn into the same type of situation without the proper safeguards. In the end, I would be in favor of the loss of attorney/client privilege in times of extreme threat to national security. I do believe that proper safeguards and procedures would have to be put into place first to ensure that this action isn't taken lightly and that people are secure in their civil liberties.