Q+A: What does Petraeus bring to Afghan war effort?

WASHINGTON (Reuters) - The choice of General David Petraeus to replace disgraced commander Stanley McChrystal ensures that President Barack Obama's 6-month-old war strategy will be executed as planned without interruption.

WHY PETRAEUS?

Petraeus, credited with salvaging the U.S. war in Iraq, has enormous credibility in Washington and has been deeply involved in shaping Afghan war strategy as the head of U.S. Central Command. There is perhaps no one in the U.S. military with more star power than Petraeus, an asset that could prove indispensable in fending off growing doubts about the war.

WHAT DOES IT MEAN FOR OBAMA'S STRATEGY?

Petraeus firmly believes the strategy in place to reverse Taliban momentum is the right one.

Widely seen as the father of modern counterinsurgency (COIN) doctrine, he oversaw development of the COIN field manual on which Obama's revised Afghan war strategy was based.

WHAT DOES IT MEAN ON THE GROUND?

No one was as immersed in the details of U.S. military plans as McChrystal, but Petraeus has overseen the effort, including planning for a major campaign to secure the Taliban birthplace of Kandahar, which is getting under way more slowly than planned.

Petraeus was a frequent visitor to the region who has built strong relations not just with the Afghan government but with authorities in neighboring Pakistan whose support is critical to the war effort.

Petraeus has been a strong advocate of pairing counterinsurgency principles with aggressive use of U.S. special operations forces.

WHAT'S PETRAEUS'S OUTLOOK ON THE WAR?

Petraeus has been careful in his public statements about not raising expectations for turning the tide quickly in Afghanistan, stressing the road ahead would be long and hard.

In testimony this month to a Senate committee, Petraeus said counterinsurgency operations amounted to a "rollercoaster experience."

"There are setbacks as well as areas of progress or successes. It is truly an up and down when you're living it, when you're doing it even from afar, frankly. But their trajectory, in my view, has generally been upwards despite the tough losses, despite the setbacks," he said.

HOW ARE HIS RELATIONS WITH THE WHITE HOUSE?

Petraeus runs a tight ship, believes strongly in adhering to the chain of command, and does not tolerate the kind of backbiting that brought down McChrystal, aides say.

He has made clear in testimony that while he will offer his candid military advice to the president in private, he will firmly support whatever decision the commander-in-chief makes.

(Reporting by Adam Entous and Phil Stewart; editing by Patricia Wilson and Doina Chiacu)