Firefighters, predicting victory, struggled to surround a major Idaho fire, one of the last of the hundreds of Western infernos that scorched forest and range lands with a total area larger than Rhode Island. An electrical storm rolled across Idaho, triggering 21 new fires that were controlled by Boise National Forest firefighters or burned themselves out by midday. Doc Smith, in charge of 1,400 firefighters battling Idaho's 18,000-acre Anderson fire, predicted that the blaze would be tamed this weekend. In Washington, several families were warned to prepare for evacuation as that state's largest fire grew to 3,200 acres when winds gusting up to 30 m.p.h. blew flames across fire lines on the Colville Indian Reservation.