WASHINGTON - Stretched thin by four years of war, the Army is adding three months to the standard yearlong tour for all active-duty soldiers in Iraq and Afghanistan, an extraordinary step aimed at maintaining the troop buildup in Baghdad.

The change, announced Wed-nesday by Defense Secretary Robert Gates, is the latest blow to an all-volunteer Army that has been given ever-shorter periods of rest and retraining at home between overseas deployments.

Rather than continue to shrink the at-home intervals to a point that might compromise soldiers