WASHINGTON — President Obama, eager to turn the page after more than a decade of war, said Friday that beginning this spring American forces would play only a supporting role in Afghanistan, which opens the way for a more rapid withdrawal of the troops.

Though Mr. Obama said he had not yet decided on specific troop levels for the rest of the year, he said the United States would accelerate the transition of security responsibilities to the Afghans, which had been set to occur at the middle of the year, because of gains by Afghan forces.

Mr. Obama also made it clear that he planned to leave relatively few troops in Afghanistan after the NATO combat mission ends in 2014, saying those forces would be narrowly focused on advising and training Afghan troops and hunting down the remnants of Al Qaeda.

“That is a very limited mission, and it is not one that would require the same kind of footprint, obviously, that we’ve had over the last 10 years in Afghanistan,” Mr. Obama said after a meeting with the Afghan president, Hamid Karzai, at the White House.