The author of "The Age of Jackson" turns now to the Age of Roosevelt, a four-volume study, of which the present book represents the substantial first installment. Actually it serves as a prologue and concludes with F.D.R.'s inauguration in March 1933; the principal theme is the abrupt reversal from prosperity to depression and the ensuing temper of fear, bewilderment and disaffection. Mr. Schlesinger's narrative is tied very closely to the activities, statements and asides of leading political figures, a method which will doubtless evoke some lively objections, but which produces an extremely vivid portrait of the times.