What, one wonders, can Sidney Alexander add to all that's been written about the painter-laureate of old Vitebsk--from, most pertinently, his early autobiography to Franz Meyer's massive 1964 life-and-works--and can it possibly justify a ""general biography"" of 500 pages? Well, Alexander does have something to add--details of the artist's liaison with Virginia Haggard MacNeil, allegedly suppressed by former son-in-law Meyer; and he also works over the art scenes of fin de siecle St. Petersburg, pre-WW I Montmartre, postwar Montparnasse, and so on--that same ""agitated, burning, and often miserable existence of the hive"" from which the ""loner"" Chagall is said to have ""kept apart."" Repeatedly said, in fact, for much of the ballast is repetition of the same ideas in virtually the same words (three times, for instance, we read that ""unlike the sedentary Picasso, Chagall is the wandering Jew"") as Alexander retraces his heavy steps, stressing the inarguable constancy of Chagall's Russian-Jewish themes, vacillating ponderously on the merit of his generally lamented later work, and persistently passing judgment on the man. Unable (presumably) to interview Chagall, he has pieced together his life from Chagall's own account (phrases, sentences, even whole paragraphs are incorporated, changed only slightly if at all, without attribution), from previous biographies, and from numerous interviews; but much of the conflicting evidence is unreconciled and simple matters of fact settled by Meyer are presented as mysteries. More dubious still is Alexander's use of Virginia MacNeil's Francoise-Gilot-like memoir to discredit Chagall--their seven years together occupy 46 pages--and also his present wife. From that episode, and Alexander's own unhappiness with the Jewish artist's church decorations, comes a picture of Chagall as ""totally self-involved"" and distinctly unsympathetic. Were it not for the occasional contribution of a Meyer Schapiro, who takes his friend Chagall as he finds him, the book would be as ill-considered as it is ill-wrought.