V!RGINIA WOOLF`s favourite reading material ("when I`m incapable of Shakespeare") was autobiography. Of Course letters are also a form of autobiography, and perhaps even more revealing because they`re intended for the eyes of personal acquaintances, not the general public. Although Woolf determinedly shied away from setting down her memoirs, she left (along with her diaries) a wealth of correspondence. Joanne Trautmann Banks shared the task of editing the six volumes of Woolf`s complete letters, which were published from 1975 to 1980; in Congenial Spirits (Harcourt Brace Jovanovich (Lester & Orpen Dennys), 472 pages, $24.95 cloth) she offers a selection that suffers little in the distillation. Woolf once wrote to one of her correspondents that she believed letters were meant to "give back a reflection of the other person." But how much the epistolary "mirrors" collected here -- with their sparkle of language and sometimes malicious wit, their lively observations on private and public matters -- also reflect of one of this century`s greatest writers.