ASHINGTON, May 12 — The Central Intelligence Agency has used coercive interrogation methods against a select group of high-level leaders and operatives of Al Qaeda that have produced growing concerns inside the agency about abuses, according to current and former counterterrorism officials. At least one agency employee has been disciplined for threatening a detainee with a gun during questioning, they said. In the case of Khalid Shaikh Mohammed, a high-level detainee who is believed to have helped plan the attacks of Sept. 11, 2001, C.I.A. interrogators used graduated levels of force, including a technique known as "water boarding," in...