Deep in a remote, fog-layered hollow near Sugar Grove, W.Va., hidden by fortress-like mountains, sits the country's largest eavesdropping bug. The station's large parabolic dishes secretly and silently sweep in millions of private telephone calls and e-mail messages an hour. Run by the ultrasecret National Security Agency, the listening post intercepts all international communications entering the eastern United States. Another N.S.A. listening post, in Yakima,Wash., eavesdrops on the western half of the country. According to John E. McLaughlin, who as the deputy director of the Central Intelligence Agency in the fall of 2001 was among the first briefed on the program, this eavesdropping was the most secret operation in the entire intelligence network, complete with its own code word - which itself is secret. Jokingly referred to as No Such Agency," the N.S.A. was created in absolute secrecy in 1952 by President Harry S. Truman. But the agency is still struggling to adjust to the war on terror. At home, it increases pressure on the agency to bypass civil liberties and skirt formal legal channels of criminal investigation. Originally created to spy on foreign adversaries, the N.S.A. was never supposed to be turned inward.