STRAIGHT ON TILL MORNING The Biography of Beryl Markham By Mary S. Lovell St. Martin's. 408 pp. $16.95

ONE OF THE more improbable stories in recent publishing history began about four years ago, when a publisher on the West Coast, North Point Press, decided to reprint a little-noticed memoir by a forgotten woman, Beryl Markham, entitled West With the Night. The new edition was reviewed rather more widely than paperback reprints usually are, favorably in all instances, and sold a modest few thousand copies. Then a documentary about Markham was syndicated on public-television stations, and suddenly the memoir was a best seller. By now several hundred thousand copies have been sold, and West With the Night has achieved the status of minor classic.

It has almost all the right ingredients. It is set in Africa during the 1920s and '30s, the period recently romanticized by the popular movie about Karen Blixen and Denys Finch Hatton, Out of Africa. It is the story of a brave and pioneering woman whose career is a model for women determined to set out on their own. It is a lyrical tribute to the beauties -- and the dangers, too -- of solo flight, at which Markham was uncommonly accomplished. And, by no means the least, it is a book that ends on a note of mystery, leaving the reader eager for more information than Markham herself provides about her personal and romantic life.

This mystery is addressed by Mary S. Lovell in Straight On Till Morning, the first biography of Markham, who died in Africa last year at the age of 84. Most readers are likely to feel that Lovell more than satisfies their curiosity. Though Straight On Till Morning is overlong, repetitious, artless and adulatory to an extreme, it is also scrupulous and thorough. In her search through the aspects of Markham's life that the memoirist herself chose to overlook, Lovell leaves scarcely a sheet unturned; and as she demonstrates quite conclusively, the sheets turned with astonishing frequency.

Apart from her accomplishments as aviator and trainer of racing horses, Markham was notable primarily for her erotic conquests. Though Lovell issues the disclaimer that "if the stories repeated to me were all true, Beryl would never have risen from a reclining position between the ages of fourteen to eighty-four," she went through spouses and lovers at a rate that would give pause to Artie Shaw or Zsa Zsa Gabor. From her first marriage at the age of 16 until well into her later years, Markham leaped in and out of bed with what the football coaches call reckless abandon; and though from time to time she indulged herself in a grand passion, for the most part these entanglements seem to have been little more to her than moments of release -- her attitude toward sex, as one of her friends observed, was what we customarily think of as masculine.

She was tall, slender and, in the fashion of certain angular British women, quite pretty -- though not pretty enough to pass a screen test to play herself in an adaptation of West With the Night that, in the end, was never filmed. Though she had feminine charms in abundance, she had been raised in Kenya virtually as a boy and, as an adult, she persisted in habits of dress and behavior more commonly associated with men than women. In style if not in sexual preference she was androgynous, a point overlooked by Lovell but emphasized in almost every photograph of Markham she reproduces. Her description of the 16-year-old Beryl is a portrait of the woman as well:

"She was fearless, strong and physically able to undertake any task she set herself. She was thoroughly at home in her surroundings and as at one with her adopted country as it is possible to be. She had great ability and was competent and knowledgeable at her work; and she had a unique facility for developing relationships with animals. What she lacked was the ability to handle human relationships. . . . In consequence she was a complex mixture of physical self-confidence and emotional awkwardness."

Had she been otherwise, she most certainly would not have accomplished the feat for which she was briefly noted in her lifetime: the east-west transatlantic solo flight, undertaken in 1936 when she was 33, that is the principal subject of West With the Night. A person of more complex and introspective turn of mind surely would have perceived the near-insuperable risks of the project and found other ways to achieve the fame that Markham sought. But for Markham it was a simple matter of getting on with the business at hand; only when it was over, and she was sailing to England across the eternal ocean, did she realize "that if she'd first crossed the Atlantic by sea she'd never have dared to fly across it."

She was a difficult and insensitive person, yet she was hardly without wit or charm. She was in severe need of both, for she was constantly short of money. Except for a few years late in life, when she became highly successful as a horse trainer and dominated the Kenyan race meetings, "all her adventures and travels were carried out without money, and she quite blatantly opened accounts with no thought of how she was to pay them." Over and again she relied on the kindness of friends -- and strangers, too -- for lodging and financial support; what is remarkable is how often such assistance was given, and how gladly. Markham may have been insensitive in human relations, as neglectful motherhood and three broken marriages attest, but she knew how to get on with people when circumstances gave her no alternative.

She seems, in fact, to have been a character rarely encountered in life or in art: the female equivalent of a rogue. The term is commonly associated with an adventuresome, physically active male who is part scoundrel and part charmer; but since that is precisely what Markham was, we must credit to her account in feminist chronicles not merely the epic transoceanic flight but also the embodiment of female roguery. On the basis of Lovell's characterization of her, it seems a judgment Markham would have cherished.

Lovell is so earnest and good-humored a biographer that it is easy to slough off her book's faults, but it must be noted that they are numerous. Her prose is graceless and from time to time ungrammatical; her repeated use of "whilst" is a grating anachronism, at least to American ears. She has difficulty distinguishing the relative importance of themes and events in Markham's life, so far too much space is devoted to horse-training gossip and other trivia; in general, she is too infatuated with her research and too willing to publish the results undigested. And her repeated mention of herself in a book that is, after all, about someone else is distracting, annoying and wholly unnecessary.

But what all these complaints add up to is that a good book should, and could, have been so much better; if ever a book could have profited from strenuous editing, Straight On Till Morning is it. It remains, though, that Mary Lovell has done a tremendous amount of original research and has used it to paint a vivid and convincing portrait of a woman who was that rare creature, an original.