The CIA's top counterterrorism officer was relieved of his position yesterday after months of turmoil atop the agency's clandestine service, according to three knowledgeable officials. Robert Grenier, who spent most of his career undercover overseas, took charge of the Counterterrorism Center about a year ago after a series of senior jobs at the center of the Bush administration's national security agenda. When al Qaeda struck the World Trade Center and the Pentagon on Sept. 11, 2001, Grenier was station chief in Islamabad, Pakistan. Among the agency's most experienced officers in southwest Asia, Grenier helped plan the covert campaign that preceded...