PHOTOS BY ARTHUR HO RWITZ Hannah is a 26-year- old workhorse. She doesn't pull wagons or plow fields. Instead she carries Israel's broken victims of terrorism, military veterans with head wounds, survivors of auto accidents, senior citizens ravaged by strokes and even blind elementary-school children. Through her patience and the guid- ance of her trainers, this chestnut-brown mare helps the dis- abled find new hope and a way to break through, to be free. ARTHUR M. HORWITZ ASSOCIATE PUBLISHER