The US Army is slashing the size of its force by about 24,000, or almost 5 percent, and restructuring to be better able to fight the next major war, as the service struggles with recruiting shortfalls that made it impossible to bring in enough soldiers to fill all the jobs. The cuts will mainly be in already-empty posts — not actual soldiers — including in jobs related to counterinsurgency that swelled during the Iraq and Afghanistan wars but are not needed as much today. About 3,000 of the cuts would come from Army special operations forces. At the same time, however, the plan will add about …