MARY SHELLEY By Muriel Spark William Abrahams/Dutton. 248 pp. $19.95 THE JOURNALS OF MARY SHELLEY 1814-1844 Edited by Paula R. Feldman And Diana Scott-Kilvert Oxford University Press. Two vols. 735 pp. $84

IT IS RARE for an author long dead to be re-evaluated and raised to a more prominent position in the hierarchy of letters. It happened to John Donne, under the influence of T. S. Eliot. Under the influence of no one more eminent than the Common Reader has Mary Shelley been restored to favor, some 130 years after her death.

Once, Mary Wollstonecraft Shelley's name was merely one attached to copies of her novel Frankenstein, or to those extraordinary movies, all myth and mayhem, starring Boris Karloff -- and attached rather insecurely, since in her lifetime that most popular novel never bore her name on its title page. Nor, for that matter, did any of her five other novels. Secrecy was one of her characteristics.

Now she has returned to renown, and not only at the behest of feminism. Her second-best novel, The Last Man, was recently reprinted, studies of Frankenstein emerge regularly from learned presses, while her letters are appearing in an awesomely complete three-volume edition. It is a pleasure now to have her journals in print at last and a reissue, much revised, of Muriel Spark's discerning biography.

One of the attractions of Mary Shelley's life (1797-1851) is the way she invites curiosity and analysis; her books provide keys to her life as her life provides a key to her books. Singular misfortunes and success were hers as much as Frankenstein's.

The distinguished feminist, Mary Wollstonecraft, died giving her birth, and in consequence she suffered a rather comfortless childhood. She fell in love with the poet Percy Bysshe Shelley and eloped with him from England to the continent, aged 16, accompanied by Claire, her half-sister. Mary was to suffer miscarriages, probably due to malnutrition, and her children died, all but one. Suicides and threats of suicide surrounded her. She was often ill and had good reason to suspect Shelley's unfaithfulness with Claire.

Shelley was drowned only six years after their marriage. Never did widow mourn so deeply -- undoubtedly she suffered from the guilt which so often accompanies bereavement. Never did widow of literary man show such conscientious concern to preserve every scrap of his writing (widows more often play fiercely destructive roles). She never married again, supporting herself, as the saying is, by her pen. "Mary Shelley shall be written on my tomb."

HOWEVER magnificent his poetry, Shelley was volatile and irresponsible as a person. Claire was an encumbrance. William Godwin, Mary's father, was cold-natured and (almost as bad) impoverished. Lord Byron, whom the lovers encountered in Italy, was the eternal Lord Byron.

The behavior of these Romantic figures is in many respects modern, undated. Talentless Shelleys spring eternal. Muriel Spark takes a sensible view of the whole matter. From now on, she ranks among the chief supporters of Mary Shelley. She is inclined to poke fun at Shelley -- would Mary had done so more often! About Godwin she is just. She passes rather superficially over the possible Shelley-Claire involvement; Richard Holmes, in his now standard life of Shelley, Shelley: The Pursuit, is more alert to the complexities of that relationship.

But it is on Mary that Spark concentrates. There were two sides to Mary Shelley, a deeply Romantic and moody side inherited from her adventurous mother and a rather chilly nonconformist side inherited from her father (Godwin being the son of a nonconformist minister). The Romantic side flourished until the shock of Shelley's death, which came just after Mary herself nearly died. Then a more sorrowing creature took over.

"I am much of a self-examiner," exclaims Mary to her journal. She confessed to Claire, long after Claire's child by Byron was dead, that she was pursued all her life by lowness of spirits. The orphaned creature she felt herself to be was, of course, touchingly dramatised in the shape of Victor Frankenstein's monster. She goes on to say, "I need to be a little bit tipsy -- this is a sad confession but a true one; any thing of emotion that quickens the flow of my blood makes me not so much a happier as a better person."

In her brisk, commonsense way, Spark suggests that had there been more wine in Mary's life there might have been fewer tears. Knowing Shelley went to everyone's head; once he was dead to Mary, the intoxication had to stop.

Spark's book is divided in two. The second half is a critical one, discussing Mary Shelley's writing rather than her life. Frankenstein is paid due attention, with praise for the conflict between Frankenstein and his creation, censure for the weakness of the rest of the characters, and the observation that what is melodramatic is denuded of melodramatic elaboration. Proper attention is also paid The Last Man, which Spark sees as a fulfillment of what Godwin failed to achieve in the novel. Her discussion of this long story, which is often heavy going, forms one of the strong points of her book, and should persuade many readers to seek it out.

Mary herself spent little time discussing her writings. One might read her journals carelessly without gathering that she was a writer. Judgments on other writers are few, although she read abundantly. The newly edited journals -- a valuable addition to Romantic studies -- provides lists of all the reading she and Shelley got through, separately or together.

In general, Mary strikes an impersonal note: Others might read her journal -- the dreaded Claire, for one. Symbols are occasionally used instead of Claire's name. But, like Thomas Hardy, Mary Shelley is a secretive person. "A marriage takes place on the 29th" covers her wedding day. When their beloved son William dies in Italy in June 1819, there is no entry; entries do not resume until August. One must read into the silences (though to Leigh Hunt she writes, "I ought to have died on 7th June last").

The entry for 26 Sept. 1818 reads, "An idle day." It conceals the fact that her baby Clara was buried. Mary's grief could find no voice.

Not on account of this cryptic tendency alone are the notes that editors Feldman and Scott-Kilvert provide essential. This is a fine scholarly edition, representing much research. I detected only one minute slip, in note 4 on p. 148, where an incorrect page reference is given to the edition of the letters, edited by Betty T. Bennett. Rewarding though the journals are to any Shelley-watcher, it must be said that reading is greatly enchanced if one has those letters by one's side.

Although Mary was neither a humorist nor a student of social mores, a lighter tone occasionally breaks in. She attends the coronation of William IV in Westminster Abbey in 1831. "They were so stingey the poor king was obliged to poke with his pen -- and the Duke of Devonshire to tilt the inkstand -- to get ink enough to write his name."

Her journals contain much of Mary Shelley's troubled life. Yet, even with the painstaking notes, some things remain unexplained. Mary still slips away into the shadows, as no doubt she often did when alive.

Brian Aldiss' most recent books include the Helliconia trilogy and "Trillion Year Spree," a history of science fiction.