When Porter J. Goss resigned on Friday as director of the C.I.A., he found himself in good company. In one way or another, the job of C.I.A. chief has confounded nearly every man who has held it.

With few exceptions, each of the previous 18 directors of central intelligence has resigned in frustration, been given his walking papers by the president or been pressured out of the agency’s headquarters seven miles up the Potomac from the White House.

“Here is one of the most peculiar types of operation any government can have,” President Dwight D. Eisenhower once said. “It probably takes a strange kind of genius to run it.”

The post was created more than 60 years ago, before the Central Intelligence Agency itself, before the cold war began. The mission was to prevent a second Pearl Harbor. The director would pull together all the military and diplomatic information the United States could gather overseas. He was to be the president’s chief intelligence officer. Together they would protect the nation from surprise attack from afar.

Things did not always work out as planned.

The threat of the Soviet Union quickly gave rise to the C.I.A. Its espionage operations tried to pierce the Iron Curtain. Its covert operations tried to change the world.

From the start, the director was supposed to serve as the editor of a secret news service and the general of a secret army, chief executive of the C.I.A. and the chairman of the board of the ever-expanding empire of American military intelligence.

Running the “intelligence community,” a chimerical construct now made up of 16 agencies and more than 100,000 people, proved almost impossible. “The job had become, frankly, too big for one person,” Mr. Goss said last year.

The first three directors of central intelligence are viewed in the agency’s own in-house histories by many as mediocrities. The fourth, Gen. Walter Bedell Smith, was aghast when his agents failed to foresee the course of the Korean War.

He was succeeded by Allen W. Dulles, who at the end of his tenure was attacked by his own commander-in-chief, President Eisenhower, who said he had “suffered an eight-year defeat” in his fight to make the C.I.A. deliver trustworthy intelligence.

Dulles led the C.I.A. into its disastrous invasion at the Bay of Pigs; President John F. Kennedy dismissed him after a decent interval.

The next director, John McCone, was tuned out by President Lyndon B. Johnson when he tried to report the downward course of the Vietnam War. A successor, Richard Helms, was turned out by President Richard M. Nixon after he refused to conceal the crimes of Watergate.

Mr. Helms, admired by his successors as the greatest director of all, remarked on the deep disconnect between the C.I.A. and the White House in a posthumously published 2002 memoir: Except for the first President George Bush, who served for 11 months as director of central intelligence in 1976, Mr. Helms noted, no American president has had more than a slight idea how clandestine operations are conceived and run.

His critique was underscored when President Ronald Reagan authorized his director of central intelligence, William J. Casey, to sell American arms to Iran as a ransom for American hostages. The uproar paralyzed the agency at the close of the cold war. Mr. Casey’s top deputy and eventual successor, Bob Gates, was asked by a photographer at his 1987 nomination hearings what he thought of the post. He replied with the title of a country-and-western hit: “Take This Job and Shove It.”

In an interview on the occasion of the C.I.A.’s 50th anniversary, in 1997, Mr. Helms warned that the end of the cold war had unmoored the C.I.A. “The only remaining superpower doesn’t have enough interest in what’s going on in the world to organize and run an espionage service,” he said. “We’ve drifted away from that as a country.”

President Bill Clinton’s first director, R. James Woolsey, was hired after the briefest possible conversation and saw the president in private precisely twice in the next two years. His successor, John M. Deutch, was scorned by many of the spies who worked for him. For a while, the turnover at the top was head-spinning — directors came and went almost annually. When Mr. Goss’s predecessor, George J. Tenet, took office in 1997, he was the fifth man in charge in six years.

“It is impossible to overstate the turbulence and disruption that that much change at the top caused in this organization,” said Fred Hitz, the C.I.A.’s inspector general in the 1990’s.

Mr. Tenet stayed on after the C.I.A.’s false conclusions that Iraq had unconventional weapons convinced millions of Americans that something was deeply flawed at C.I.A. headquarters. The flaw, two national commissions concluded, lay in the post of director itself. American intelligence was not an orchestra but a cacophony.

“We lurch from near disaster to near disaster,” said James Monnier Simon Jr., the assistant director of central intelligence for administration from 1999 to 2003. John MacGaffin, a 31-year C.I.A. veteran and a senior White House counterterrorism consultant, warned recently that “the national counterterrorism effort more closely resembles kids’ soccer than professional football.”

When Mr. Goss took over in September 2004, he addressed C.I.A. officers in a state of exhilaration. His powers, he announced, would be “enhanced by executive orders” from the president. He proclaimed he would be the president’s intelligence briefer, the head of the C.I.A., the director of central intelligence, the national intelligence director, and the chief of a new National Counterterrorism Center.

But within months, all those roles and missions but one were taken away. The job of director of central intelligence was dissolved a year ago in favor of a new national intelligence czar, John D. Negroponte, who has taken over the tasks of briefing the president and controlling American liaison with foreign intelligence services. Mr. Goss had become, literally, the last director.

And with his resignation, it may be that the Central Intelligence Agency is no longer central in the American government.

“In the wake of the Iraq war, it has become clear that official intelligence analysis was not relied on in making even the most significant national security decisions,” Paul R. Pillar, a senior C.I.A. analyst who retired last year, wrote in the March/April issue of Foreign Affairs.

“Our intelligence is now devoid of credibility,” in the words of David Kay, who as the special adviser to the director of central intelligence led the search for unconventional weapons in Iraq in 2003 and 2004. “We as a nation must address that, or Iraq is prologue to a much more dangerous time than anything we have ever seen.”