U.S. Defence Secretary Robert Gates addresses the Association of the United States Army 2009 annual meeting in Washington on Monday. (Charles Dharapak/Associated Press)

The U.S. military will fall in line with whatever strategy President Barack Obama decides on Afghanistan, despite a fierce policy divide inside the White House over the issue, Defence Secretary Robert Gates said Monday in Washington.

The debate over sending as many as 40,000 more U.S. troops to Afghanistan is a major element of the strategy overhaul that senior administration policy advisers will consider this week as they gather for top-level meetings on the evolving direction in the war.

At issue is whether U.S. forces should continue to focus on fighting the Taliban and securing the Afghan population, or shift to more narrowly targeting al-Qaeda militants believed to be hiding in Pakistan, using unmanned spy planes and covert operations to kill them.

Leaving Afghanistan is not an option that Obama is considering, White House spokesman Robert Gibbs said Monday.

The top three U.S. military commanders overseeing the war in Afghanistan favour continuing the current fight against the Taliban, which could take as many as 40,000 additional U.S. troops.

Gates's comments came after the top U.S. and NATO commander in Afghanistan, army Gen. Stanley McChrystal, bluntly warned a London audience last Thursday that Afghan insurgents are gathering strength and any plan that falls short of stabilizing Afghanistan "is probably a shortsighted strategy."

NATO contributes roughly two-thirds of the more than 100,000 international troops in Afghanistan, including 32,000 from the U.S. and nearly 3,000 from Canada. Another 36,000 American soldiers in the country are under direct U.S. command.

Canada is due to pull its troops out of combat roles in Afghanistan by 2011.