David Petraeus was sworn in Tuesday as head of the CIA to direct the civilian covert war against Al-Qaeda after years of command in Iraq and Afghanistan as America's most influential general.

Petraeus, 58, who succeeds Leon Panetta, now the defense secretary, hung up his army uniform less than a week ago after a 37-year military career to take on the new role as spymaster.

"Duty, honor and country," said Vice President Joe Biden as he swore in Petraeus at the White House.

"The day I met you in Afghanistan, those words came to mind. You have had a truly distinguished career, general. You've excelled in every single thing you've done."

Dressed in a business suit with a burgundy tie, Petraeus swore the oath of office on a Bible in the Roosevelt room of the White House, instead of CIA headquarters in Langley, Virginia.

Biden, who has had sharp policy differences with Petraeus in the past, said the White House venue was chosen "because there's literally no time to waste. The president wants him on the job."

"Thanks to President (Barack) Obama for his confidence in an old soldier. I had a great retirement. That's been a terrific week," Petraeus quipped.

A voracious consumer of intelligence, Petraeus brings to his new job his experience as a commander who melded military and intelligence operations to an extraordinary degree in both Iraq and Afghanistan.

The CIA has conducted a lethal and often controversial campaign of drone attacks that Panetta contends has brought Al-Qaeda to the brink of strategic defeat.

But Petraeus also inherits tense relations with Islamabad and its intelligence services, which were infuriated by a May 2 raid by US Navy SEALs that killed Al-Qaeda leader Osama bin Laden deep inside Pakistan.

The Pakistan's Inter-Services Intelligence Agency reacted by arresting Pakistani informants who helped the CIA prepare for the raid, and US suspicions of Pakistani complicity in harboring bin Laden have run high.

Nevertheless, there were signs of a thaw over the weekend, after the Pakistani army announced it had arrested a senior Al-Qaeda operative with the help of the US intelligence agency.

As CIA director, Petraeus's responsibilities extend far beyond Al-Qaeda to some of the hardest and most complex targets facing US intelligence -- North Korea, Iran and China among them.

Ambitious and supremely disciplined, Petraeus has sometimes irritated fellow commanders, earning the nickname "King David." But his successes on the battlefield won him fame and the confidence of US presidents.

President George Bush put him in command of US forces in Iraq in 2007 as the country was descending into civil war and Petraeus managed to salvage the situation with a controversial troop surge.

Whether the surge in Iraq turned the tide is still under debate, with critics arguing that violence receded because Al-Qaeda's brutal tactics alienated Sunni tribal leaders.

Obama turned to Petraeus to take command in Afghanistan in mid-2010 as security conditions deteriorated there despite a surge of some 30,000 US troops.

Before stepping down in July after nearly a year as head of the US-led force there, Petraeus claimed progress against the Taliban as American troops rolled back the insurgents in the south while Afghan security forces expanded.

But the insurgency has proved resilient, and the jury is still out on the general's tenure there.

Still, when Petraeus retired from the military on August 30, Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, hailed the four star general as one of the "giants" in US military history.

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