South America's masses of illiterate poor have been silent thus far because they are unorganized and resigned to exploitation: ""the very poor seldom make revolutions"" of any kind. Cuba was one of the better-off nations, down there. But the few remaining dictatorships are shaky and inklings of the rising demands of the rest of the world's underprivileged are beginning to penetrate the backlands. Propping up ""anti-Communist"" dictatorships like the one in Guatemala will, says Mr. Shapiro, simply assure more revolutions in the Cuban style. The more enlightened leaders, some of them ""elected"" where the larger share of the populace is not qualified to vote, are left a legacy of greed and corruption to overcome first. South American armies stand ever ready to preserve the status quo, should a new administration prove dangerously rermist. One-crop economies are prey to inflation. As for democracy;- a full belly seems to take precedence over civil liberties. Mr. Shapiro's analysis deserves the hole gamut of complimentary adjectives; it is especially important for the way it elates the facts of South American economic and political life to realistic expectations for the Alliance for Progress.