A milestone found

Our Nig, or Sketches from the Life of a Free Black, by Harriet E. Wilson. With an Introduction and Notes by Henry Louis Gates Jr. New York: Random House. 139 pp. (plus introduction, notes, appendices, bibliography). $10.95 in hard cover, $4.95 in paperback.

The projected publication of ''Our Nig'' was hailed earlier this year by the New York Times as a ''black literary landmark.'' Certainly the republication of the first novel published by a black woman is a newsworthy event. Whether or not it qualifies as a ''literary landmark'' remains to be seen. It is, however, a very good book.

Prof. Henry Gates Jr. of Yale University claims in his introduction that the novel was ignored when it was published in 1859, because it explored themes that would have embarrassed Northern blacks and abolitionists: interracial marriage, racism in the North, and blacks who posed as fugitive slaves to hustle a living.

Although these elements are mentioned in the novel, they are not the focus of the book and are never treated with the attention that would make them themes. Perhaps 19th-century blacks and abolitionists did ignore the novel because of these elements. But it is also possible that the novel never circulated widely and did not make its way into the hands of those who might or might not have been offended.

''Our Nig'' is worthy enough on its own not to need ersatz drama created around it, which can only raise expectations that the novel does not meet.

It is a novel of the sentimental genre common in the 19th century. ''Our Nig'' tells the story of a young mulatto girl, abandoned by her white mother and black stepfather, who becomes an indentured servant for a New England white family. The girl is cruelly mistreated by Mrs. Bellmont and her oldest daughter, until she is broken in body and spirit. The novel chronicles her suffering with an immediacy that is admirable.

What makes it worthy of attention now as something more than a literary and historical curiosity is the author's ability to write and the power of her characterizations. We sympathize with Frado, the mulatto girl, detest Mrs. Bellmont and her oldest daughter, and are impatient with Mr. Bellmont and his sons, well-meaning, but weak men. The characters come vividly to life, despite the tone of moralizing that typified 19th-century writing.

The author knew how to craft a sentence bristling with irony, as in describing Mrs. Bellmont as ''not as susceptible of fine emotions as her spouse.'' When irony becomes bitterness, the author maintains literary control, as when Frado is about to marry a bogus fugitive slave: ''She opened her heart to the presence of love - that arbitrary and inexorable tyrant.'' Anyone coming to the novel expecting the broad social canvas of 19th-century New England will be disappointed. It offers a microcosm, deftly and movingly rendered. One cannot generalize about free blacks from reading this novel, but you will come to know intimately the suffering of one black woman. This achievement qualifies ''Our Nig'' for the accolade literature.

The novel has its own surprising ironies, though it shouldn't be surprising to find a 19th-century woman, even though she is black, expressing prejudices typical of the age. Mag, Frado's real mother, has to compete for work with ''foreigners who cheapened toil,'' and when the black, Jim, asks Mag to marry him, his most convincing argument is to ask if she'd rather have ''a black heart in a white skin, or a white heart in a black one?''

Little is known about the author, Harriet E. Wilson. Professor Gates's exhaustive research uncovered that she was born in New Hampshire and at the time of the book's publication was living in Boston. The impetus for writing the novel came not from a literary impulse, but from the desperate need to earn money to support her young son, who died six months after the book's publication.

This much is evident from reading ''Our Nig'': Harriet E. Wilson was a good writer, and as Professor Gates notes, she was better at the craft of fiction than any of her black male contemporaries, many of whom were better educated. It was not only her loss but ours that the circumstances of her life were so difficult that there was no opportunity for her to become the writer ''Our Nig'' indicates she could have been.