WASHINGTON, Sept. 16 - The chief of the Army Reserve warned on Thursday that at the current pace of operations in places like Afghanistan and Iraq, the Army faced a risk of running out of crucial specialists in the Reserves who can be involuntarily called up for active duty. The remarks by the officer, Lt. Gen. James R. Helmly, throw a spotlight on the military's existing mobilization authority, under which Reserve and National Guard personnel can be summoned to active duty for no more than a total of 24 months, unless they volunteer to extend their tours. As military operations...