By David Morgan

WASHINGTON (Reuters) - Defence Secretary Robert Gates on Monday replaced the top U.S. and NATO commander in Afghanistan and picked a former special forces commander to oversee President Barack Obama's military strategy against a growing Taliban insurgency.

Gates asked for the resignation of Army General David McKiernan less than a year into a command that normally would last 18 to 24 months after concluding the new U.S. strategy in Afghanistan required fresh military thinking.

Gates recommended Army Lieutenant General Stanley McChrystal, a former Green Beret, to take over command of the 45,000 U.S. troops and 32,000 other forces from other NATO countries now in Afghanistan.

McChrystal, the director of the U.S. military's Joint Staff, must be nominated by Obama and confirmed by the U.S. Senate before he can take up the post.

Gates also named Lieutenant General David Rodriguez as deputy commander of U.S. forces in Afghanistan. Rodriguez was lauded by Pentagon officials for a counterinsurgency effort he led in eastern Afghanistan while commanding the Army's 82nd Airborne Division.

"This is the right time to make the change," Gates told reporters at the Pentagon after returning from his latest trip to Afghanistan.

"The way I look at this is as McChrystal and Rodriguez as a team. They each bring tremendous skills in a variety of areas that are very pertinent to the kind of fight that we have (in) Afghanistan. And it is their combined skill set that I think gives us some fresh opportunities looking forward."

Obama "agreed ... that the implementation of a new strategy in Afghanistan called for new military leadership," White House spokesman Robert Gibbs said.