Aug. 4, 1961 - Five hundred thousand people - about one-twelfth of Cuba's population - are now enrolled in neighborhood, factory and farm "vigilance committees." In theory, these committees provide the Government with a formidable instrument for supervising the life of the Cuban people. Membership in the committees require a willingness to work fourteen hours a day, to attend rallies, to do guard duty and to acquire a "revolutionary" mentality. That mentality is defined as the mastery of Marxist-Leninist principles. The principal task of these committees is to bring their ideas to, and act as an example for, the general Cuban population.