WARTIME WRITINGS 1939-1944 by Antoine de Saint-Exupery, translated by Noah Purcell (Harcourt Brace Jovanovich: $8.95) . These letters, diary entries and miscellaneous rough drafts reveal the French pilot-novelist's state of mind during his exile from occupied France. Saint-Exupery passionately sought an active role in the fight against the Nazi occupation of France, and finally succeeded in winning an assignment to fly reconnaissance missions--an assignment that led to his death. Occasional sentences echo the themes of his novels--the love of the mail pilot for the people he serves ("Night Flight") and the majestic loneliness of the North African desert that would become a key to "The Little Prince." But the most intense passages focus on the advance of technology at the expense of spiritual values that he correctly predicted would blight the postwar world: "It is true that technical progress in modern times has linked men together like a complex nervous system. The means of travel are numerous and communication is instantaneous--we are joined together like cells of a single body, but this body has as yet no soul."