WASHINGTON — David H. Petraeus, the director of the Central Intelligence Agency and one of America’s most decorated four-star generals, resigned on Friday after an F.B.I. investigation uncovered evidence that he had been involved in an extramarital affair.
Mr. Petraeus issued a statement acknowledging the affair after President Obama accepted his resignation and it was announced by the C.I.A. The disclosure ended a triumphant re-election week for the president with an unfolding scandal.
Government officials said that the F.B.I. began an investigation into a “potential criminal matter” several months ago that was not focused on Mr. Petraeus. In the course of their inquiry into whether a computer used by Mr. Petraeus had been compromised, agents discovered evidence of the relationship as well as other security concerns. About two weeks ago, F.B.I. agents met with Mr. Petraeus to discuss the investigation.
Administration and Congressional officials identified the woman as Paula Broadwell, the co-author of a biography of Mr. Petraeus. Her book, “All In: The Education of General David Petraeus,” was published this year. Ms. Broadwell could not be reached for comment.
Ms. Broadwell, a graduate of the United States Military Academy at West Point, spent 15 years in the military, according to a biography that had appeared on her Web site. She spent extended periods of time with Mr. Petraeus in Afghanistan, interviewing him for her book, which grew out of a two-year research project for her doctoral dissertation and which she promoted on a high-profile tour that included an appearance on “The Daily Show With Jon Stewart.”
Married with two children, she has described Mr. Petraeus as her mentor.
Senior members of Congress were alerted to Mr. Petraeus’s impending resignation by intelligence officials about six hours before the C.I.A. announced it. One Congressional official who was briefed on the matter said that Mr. Petraeus had been encouraged “to get out in front of the issue” and resign, and that he agreed.
As for how the affair came to light, the Congressional official said that “it was portrayed to us that the F.B.I. was investigating something else and came upon him. My impression is that the F.B.I. stumbled across this.”
The Federal Bureau of Investigation did not inform the Senate and House Intelligence Committees about the inquiry until this week, according to Congressional officials, who noted that by law the panels — and especially their chairmen and ranking members — are supposed to be told about significant developments in the intelligence arena. The Senate committee plans to pursue the question of why it was not told, one official said.
The revelation of a secret inquiry into the head of the nation’s premier spy agency raised urgent questions about Mr. Petraeus’s 14-month tenure at the C.I.A. and the decision by Mr. Obama to elevate him to head the agency after leading the country’s war effort in Afghanistan. White House officials said they did not know about the affair until this week, when Mr. Petraeus informed them.
“After being married for over 37 years, I showed extremely poor judgment by engaging in an extramarital affair,” Mr. Petraeus said in his statement, expressing regret for his abrupt departure. “Such behavior is unacceptable, both as a husband and as the leader of an organization such as ours. This afternoon, the president graciously accepted my resignation.”
Mr. Petraeus’s admission and resignation represent a remarkable fall from grace for one of the most prominent figures in America’s modern military and intelligence community, a commander who helped lead the nation’s wartime activities in the decade after the Sept. 11 attacks and was credited with turning around the failing war effort in Iraq.
Mr. Petraeus almost single-handedly forced a profound evolution in the country’s military thinking and doctrine with his philosophy of counterinsurgency, focused more on protecting the civilian population than on killing enemies. More than most of his flag officer peers, he understood how to navigate Washington politics and news media, helping him rise through the ranks and obtain resources he needed, although fellow Army leaders often resented what they saw as a grasping careerism.
“To an important degree, a generation of officers tried to pattern themselves after Petraeus,” said Stephen Biddle, a military scholar at George Washington University who advised Mr. Petraeus at times. “He was controversial; a lot of people didn’t like him. But everybody looked at him as the model of what a modern general was to be.”
At the C.I.A., Mr. Petraeus maintained a low profile, in contrast to the celebrity that surrounded him as a general. But since the attack in Benghazi, Libya, that killed four Americans two months ago, critics had increasingly pressured him to give the agency’s account of the chaotic night. Mr. Petraeus was scheduled to testify before a closed Congressional hearing next week.
White House officials say they were informed on Wednesday night that Mr. Petraeus was considering resigning because of an extramarital affair. Intelligence officials notified the president’s national security staff. Mr. Obama at the time was on his way back to Washington from Chicago, where he had gone to receive election returns.
On Thursday morning, just before a staff meeting at the White House, Mr. Obama was told. “He was surprised, and he was disappointed,” one senior administration official said. “You don’t expect to hear that the Thursday after you were re-elected.”
The president was in the White House all day on Thursday, getting back to his old routine after months on the campaign trail. That afternoon, Mr. Petraeus came in to see him, and informed him that he strongly believed he had to resign.
Mr. Obama did not accept his resignation right away. “He told him, ‘I’ll think about it overnight,’ ” the administration official said. After months on the road, the disclosure of a career-killing extramarital affair from his larger-than-life C.I.A. director was the last thing that Mr. Obama was expecting, the official said.
The president, officials said, did not want Mr. Petraeus to leave. But he ultimately decided that he would not lean heavily on him to stay. On Friday, he called Mr. Petraeus and accepted the resignation, “agreeing with Petraeus’s judgment that he couldn’t continue to lead the agency,” a White House official said.
The White House had hoped to keep the news under wraps until after the daily briefing for the news media, but as it was reported on MSNBC, reporters checking their e-mail confronted Jay Carney, the press secretary, who tried to duck the questions.
“I think I’ll let General Petraeus address this,” Mr. Carney said. Shortly after the news broke, Mr. Obama released a statement praising Mr. Petraeus for his “extraordinary service” to the country and expressing support for him and his wife, Holly.
“By any measure, through his lifetime of service, David Petraeus has made our country safer and stronger,” the president said. Without directly addressing the affair, Mr. Obama added, “Going forward, my thoughts and prayers are with Dave and Holly Petraeus, who has done so much to help military families through her own work.”
A favorite of President George W. Bush and once the subject of intense speculation about his future as a possible presidential candidate, Mr. Petraeus managed the awkward move from a Republican administration to a Democratic one. He was one of the most telegenic faces of the military during his tenure, testifying frequently in Congress about the country’s difficult battles overseas.
Mr. Petraeus clashed with Mr. Obama in 2008 during a campaign visit to Iraq, having what David Plouffe, his campaign manager, called in his book a “healthy debate” over troop levels in the country.
But the president’s decision to tap Mr. Petraeus to command the war in Afghanistan, and later picking him to lead the C.I.A., effectively ended lingering concerns among Obama political advisers that the popular general might challenge his commander in chief during the election.
Mr. Petraeus and his wife met when he was a cadet at West Point; she was the daughter of the academy’s superintendent and a student at Dickinson College in Pennsylvania.
Holly Petraeus works for the Consumer Financial Protection Bureau, running a branch dedicated to educating military families about financial matters and monitoring their consumer complaints.
Mr. Petraeus’s resignation and the circumstances surrounding it stunned military officers who have served alongside him in war zones over the past two decades and the national security establishment he later served.
“It was a punch in the gut for those of us who know him,” said Col. Michael J. Meese, a professor at West Point who has known Mr. Petraeus for a decade and served as one of his top aides in Bosnia, Iraq and Afghanistan.
“Dave’s decision to step down represents the loss of one of our nation’s most respected public servants.” James R. Clapper, the director of national intelligence, said in a statement.
By acknowledging an extramarital affair, Mr. Petraeus, 60, was confronting a sensitive issue for a spy chief. Intelligence agencies are often concerned about the possibility that agents who engage in such behavior could be blackmailed for information.
Mr. Petraeus praised his colleagues at the C.I.A.’s headquarters in Langley, Va., calling them “truly exceptional in every regard” and thanking them for their service to the country. He made it clear that his departure was not how he had envisioned ending a storied career in the military and in intelligence.
“Teddy Roosevelt once observed that life’s greatest gift is the opportunity to work hard at work worth doing,” he said. “I will always treasure my opportunity to have done that with you, and I will always regret the circumstances that brought that work with you to an end.”
Under Mr. Bush, Mr. Petraeus was credited for helping to develop and put in place the “surge” in troops in Iraq that helped wind down the war there. Mr. Petraeus was moved to Afghanistan in 2010 after Mr. Obama fired Gen. Stanley A. McChrystal over comments he made to a reporter.
In his statement on Friday, Mr. Obama said that Michael J. Morell, the deputy director of the C.I.A., would take over once again as acting director, as he did briefly after Leon E. Panetta left the agency last year.
Among those who might succeed Mr. Petraeus permanently is John O. Brennan, the president’s adviser for domestic security and counterterrorism. Mr. Brennan was considered for C.I.A. director before Mr. Obama’s term began but withdrew amid criticism from some of the president’s liberal supporters. Another possibility is Michael G. Vickers, the top Pentagon intelligence policy official and a former C.I.A. paramilitary officer.
This article has been revised to reflect the following correction:
Correction: November 9, 2012
An earlier version of this article incorrectly stated that David H. Petraeus was expected to remain in President Obama’s cabinet. The C.I.A. director is not a cabinet member in the Obama administration.