Mr. Davis has greater credentials as a biographer of the Bouviers than skills -- he's Jacqueline's first cousin. And even though he's determined to ""call a spade a spade,"" you can be sure that he's not digging up any real family dirt. Which is not to gainsay the inevitable commercial appeal this will have. Mr. Davis' ""Portrait of an American Family""-begins five generations back in 1815 when the first Bouvier, Michel, fled to the U.S. after Napoleon's Hundred Days, settled in Philadelphia, and was both financially ambitious and philoprogenitive (twelve little ones.) It was his wife who contributed ""the aristocratic identity that was to characterize the Bouvier family in future generations"" -- a quality to which Mr. Davis is by no means immune. Shifting to New York in the next two generations, affiliating with the Drexels and acquiring great wealth, the Bouviers were dependent on John V. Bouvier as the only perpetuator of the name and promulgator of their genealogical distinctions via his sometimes wishful history Our Forebears written for his five children. Among them Jack, dashing and debonair, a great womanizer who imparted his sense of style to his daughter for whom he competed possessively after his divorce from the relatively ""nouveau"" Janet. One bad apple, brother Bud who drank himself to death. Finally the apotheosis of the Bouvier dream in Jackie -- ""elegance, poise, mystere."" Mr. Davis, a rather plebeian writer, often attempts to lend tone with unnecessary French words, continues the heroine worship of our former First Lady (""an incomparable artist in life""), justifies the Onassian alliance. He is also prone to rhetorical speculations such as ""Who knew what the future held?"" Who knows indeed -- best sellerdom?