This article is by C. J. Chivers, Alissa J. Rubin and Wesley Morgan.

KABUL, Afghanistan  After years of fighting for control of a prominent valley in the rugged mountains of eastern Afghanistan, the United States military has begun to pull back most of its forces from ground it once insisted was central to the campaign against the Taliban and Al Qaeda.

The withdrawal from the Pech Valley, a remote region in Kunar Province, formally began on Feb. 15. The military projects that it will last about two months, part of a shift of Western forces to the province’s more populated areas. Afghan units will remain in the valley, a test of their military readiness.

While American officials say the withdrawal matches the latest counterinsurgency doctrine’s emphasis on protecting Afghan civilians, Afghan officials worry that the shift of troops amounts to an abandonment of territory where multiple insurgent groups are well established, an area that Afghans fear they may not be ready to defend on their own.

And it is an emotional issue for American troops, who fear that their service and sacrifices could be squandered. At least 103 American soldiers have died in or near the valley’s maze of steep gullies and soaring peaks, according to a count by The New York Times, and many times more have been wounded, often severely.