Mr. Weltner is what his title claims. Two primary modifiers would be ""young"" and ""moderate"" -- or perhaps in the second case ""decent"" would be more exact. He's a congressman from Atlanta, Ga. His autobiography, one supposes, could be called candid; at any rate he begins with the moment he voted ""Aye"" for the Civil Rights Bill, at least partly wishing it were possible to record a ""Yes, maybe"" or a ""No, but""; and then he goes back over his 39 years of life to demonstrate the evolution of his mixed emotions. His story is a valuable one for Northerners, whatever their own feelings about civil rights, in that it expresses, succinctly and undemonstratively, the ambiguous position of all young moderate, decent white Southerners. It is perhaps even more directly aimed at the people of the South who have elected men like him -- older people, little people, in positions still more ambivalent as regards their Negro neighbors, peers, competitors. To them he says: ""If we ignore Southern history, we will relive it. If we (Negroes and whites) remain divided, we will suffer anew the old consequences.