Huge Dike Collapses in Typhoon-Struck R.P.MANILA (AP) — A major dike up to 20 feet high collapsed early Tuesday in Pampanga province in central Luzon, 40 miles from Manila.The army immediately called for the urgent evacuation of 50,-000 people from homes along the banks of the swollen Pampanga River.Heavy floods in the aftermath of Typhoon Olga, which lingered as a tropical storm in northern Luzon nearly six days after it first struck the country, sweptthrough the central Luzon provinces, major rice producing area of the Philippines.A spokesman for the 102nd Army Home Defense Center in Pampanga appealed for amphibious vehicles from Clark AB and for Philippine Air Force helicopters to help evacuate residents.Clark is about 20 miles west of the flooded area which is a low-lying marsh.The military reported the Ar-nedo Dike collapsed before dawn. The project is funded bythe World Bank and was designed as a major flood control device.The Philippine Red Cross said the death toll since the typhoon struck the Philippines Thursday was 51 persons.Officials reported heavy damage to standing crops, but the government said much of the rice harvest was completed before the storm struck.The Department of Public Information said the Arnedo Dike had overflowed Monday night,and residents of San Simon, a town of 20,000 already had moved to higher ground.Elsewhere, the governor of Nueva Ecija, north of Pampanga, reported 24 towns under water, with an estimated 10,000 persons-stranded in La Paz.A flood control station in Pampanga reported flood water rising at the rate of 60 centimeters or 23.7 inches an hour.The tropical storm lingered in northern Luzon although weathermen reported Monday they expected it to head for the South China Sea. They predicted it would remain in the Philippines at least until Tuesday evening.For the first time in five days, government and private offices opened in Manila which still was hit by heavy rains.Several thousands of passengers were still on inter-island vessels which had taken shelter in coves in Mindoro Island, 100 miles south of Manila, and had not moved for several days.Most were going to Manila.