One model for the new divisions is the agency’s Counterterrorism Center, an amalgam of undercover spies and analysts charged with hunting, and often killing, militant suspects across the globe. Once a small, occasionally neglected office in the C.I.A., the Counterterrorism Center has grown into a behemoth with thousands of officers since the Sept. 11 attacks as the C.I.A. has taken charge of a number of secret wars overseas.

But Mr. Brennan also cited another model for his new plan: the American military. He said that the Defense Department’s structure of having a single military commander in charge of all operations in a particular region — the way a four-star commander runs United States Central Command — was an efficient structure that led to better accountability.

Mark M. Lowenthal, a former senior C.I.A. analyst, said that the reorganization “is not going to go down smoothly” at the agency, especially among clandestine spies who have long been able to withhold information from analysts, such as the identity of their foreign agents. “The clandestine service is very, very guarded about giving too much information about sources to the analysts,” he said.

But Mr. Lowenthal, who said he had not been briefed about the reorganization and was basing his understanding of Mr. Brennan’s plan on news accounts, said that the new mission centers could help avoid a debacle like the intelligence assessments before the Iraq war, when analysts trusted information from sources they knew little about, and who were later discredited.

During his two years as C.I.A. director, Mr. Brennan has become known for working long days but also for being loath to delegate decisions to lower levels of C.I.A. bureaucracy. During the briefing on Wednesday, he showed flashes of frustration that, under the C.I.A.’s current structure, there is not one single person in charge of — and to hold accountable for — a number of pressing issues.