Clashes between government troops and Communist rebels in the northern and central Philippines have left 25 people dead, the military said today. Troops killed 11 rebels and suffered six dead in an encounter Monday with an undetermined number of Communist New People's Army guerrillas in the town of Claveria, 270 miles north of Manila, a military report said. A separate report said four soldiers and one rebel were killed Tuesday when a guerrilla band ambushed a military patrol on the central island of Negros, 300 miles south of Manila. In the Negros city of Bacolod, two rebels were killed in a shootout with troops Tuesday, one day after a soldier was gunned down by suspected rebels. The rebel army, which operates in most of the Philippines' 73 provinces, has been fighting for 21 years to establish a Marxist government in the country.