Some years before the inception of the Peace Corps, the Rev. James A. Robinson, a Harlem minister, set out to prove that a few hundred Americans and Canadians could reduce the ignorance Africans and North Americans have of one another's social, economic and political customs. ""Crossroads"" makes it possible for undergraduates who supply half their own expenses to spend a summer in small groups in one of several locations in East or West Africa, performing specific work projects. The author has toured representative sites and her report is a lively one. The special bearing it has on young people is obvious.