Miss Alexander's biography might be aptly subtitled Ten Years Journey Into Light. Her decade of meticulous probing, characterized by both a stubborn resistance to the slovenly data of her predecessors and an agnostic refusal to be ""mythmerized"" by O'Neill's brooding self-justification, has yielded a plenty. The tempering years end with O'Neill as recipient of the 19 Pulitzer Prize for Beyond the Horizon, so it is inevitable that a biography of one so incestuously involved with family should lay a great deal of stress on the temperers. These tempereers are not, however, the dramaturgically effective Tyrones, but the flesh and blood O'Neills. James O'Neill emerges not as the ""cheap bastard"" of his sons' invention. Ella O'Neill becomes addicted to drugs not because of Eugene's birth, but because of a breast cancer developed at a time when the palliative morphine could be purchased at the corner apothecary. (The allegedly more definitive Gelb biography, due in February, to the contrary, it is hardly conceivable that Miss Alexander has pulled a carcinoma out of anybody's bat.) Though one could ask for a few more telling adjectives and some deeper psychological dives when jumping from the specific to the general, here's the kind of basic research that will demuddle the apocryphal and demolish contemporary biographers who did not do their homework nearly so thoroughly as Miss Alexander. Watch for this one and the inevitable comparisons struck. Footnotes, anyone?