NOTHING EVER HAPPENS TO THE BRAVE The Story of Martha Gellhorn By Carl Rollyson St. Martin's Press. 544 pp. $24.95

MANY MIDWESTERNERS are stay-at-homes by nature, afflicted or blessed, depending on how you look at it, with what an Ohio friend of mine calls "the stodge factor." Uproot them for any length of time and they suffer horizon deprivation. Other Midwesterners, itchy-footed, can scarcely wait to put all that flatness behind them. Such a one is the war correspondent and fiction writer Martha Gellhorn, born in St. Louis in 1908, who in five decades of reporting, as her biographer Carl Rollyson says, has covered "virtually every conflict from the Spanish Civil War to Vietnam." The farther she has managed to escape from the banks of the Mississippi, in spite of her privileged, enlightened and loving upbringing there, the happier she always has been.

Now, in her eighties, Gellhorn lives in a cottage in North Wales where she is apparently still as glamorous as, in different ways, were the subjects of Rollyson's earlier biographies, Marilyn Monroe and Lillian Hellman. When he set out to do this book he got no cooperation from Gellhorn, who said she wished to retain her "lifelong obscurity." For a self-described recluse she has been uncommonly active, uncommonly productive and uncommonly connected. Last spring's issue of Granta carried her long and impressive report on "The Invasion of Panama." She has written six novels, six story collections, three books of nonfiction and scores of magazine articles. She has been closely associated, maritally and otherwise, with some of the least obscure names of our time.

Before she became the third of Ernest Hemingway's four wives, she consorted with Bertrand Jouvenel, who had been initiated into the mysteries of manhood by the novelist Colette. Jouvenel and Gellhorn "saw in political life an incredibly moving human drama and insisted upon treating any proposal for social or economic change in terms of human costs and benefits . . ."

Later Gellhorn was the wife of T.S. Matthews, a Time editor who didn't sound any more like a Midwestern native, though he was, than she did. "Their speech," Rollyson writes, "had a cultivated mid-Atlantic accent that made it impossible to identify them with any particular region. Their conversation was very bright, very witty." This book cries for more examples of this bright wit; it is short on dialogue and long on lumbering paraphrases. "When not at home in Wales or in her London flat," writes Rollyson, his subject "is traveling to places such as the Seychelles for snorkeling." One of her earlier homes was "sparsely decorated in a Danish Modern motif and had an open, tasteful air to it."

But if Gellhorn's tale is lamely told at times, it is still quite a story. Her early travels were smoothed with a letter to "All American Foreign Service Officers" from Franklin Delano Roosevelt, requesting "every assistance" for the correspondent, whom the president described as "an old friend of Mrs. Roosevelt's and mine." Eleanor Roosevelt and Gellhorn's mother Edna, who had worked together on social causes and programs, both "came from a generation more admirable than Martha's own. They had an incredible capacity to make people feel accepted and worthwhile."

As the Roosevelts' protegee, Martha had the run first of the Executive Mansion in Albany and later of the White House, where the first lady bestowed on her "a steady, compassionate, but sober interest in her affairs." By way of thanks, in 1951, 43-year-old Martha, who looked as smashing as ever, lured away from Mrs. Roosevelt, who was 66, her 48-year-old "special man," the unhappily-married Russian-born physician, David Gurewitsch.

Rollyson became interested in Gellhorn while researching his book on Hellman, whom Gellhorn here dismisses, along with the poet Stephen Spender, as " 'apocryphiars': falsifiers of history who build themselves up or denigrate their famous subjects . . ." These two, in Gellhorn's view, both "had claimed important relationships with Hemingway that the facts did not support." Her own relationship with Hemingway could exasperate them both. "I knew you'd get here, daughter," he said in 1937 when she finally and laboriously managed to join him in Spain -- no thanks to him -- "because I fixed it so you could." She thought he was too fat; he thought she was too fastidious, and that she "loves humanity but can't stand people." He'd tell his cronies she was "off to take the pulse of the nation." SUCH pulse-taking has always been more Gellhorn's style than domesticity. Like many journalists, she is most comfortable in short-term, middle-distance relationships, when she has an important-sounding reason to rush off somewhere else before people can find out what she's really like. Though Martha told Hemingway, in one passionate letter, that the only people she really loved were he {sic} and her mother, she could not be bothered to return to St. Louis during Edna's terminal illness: "I don't want to be here when she dies," she said: "I want to remember her as she was."

Her adopted son, Sandy, whom she discovered in an Italian orphanage when he was 15 months old, did not fare much better. "Peace," she had decided when World War II was over, "meant somehow healing the wounds of maimed and homeless children." A single parent whose trade was writing, she reasoned, had to be better than no parent at all. But Mrs. Roosevelt, considering the child's life years later, thought Sandy "was suffering from his mother's total absorption in herself . . . Gellhorn's egotism appalled her."

In many respects Gellhorn has been more taken with ideas than with realities. "One of her friends has suggested that her interest in sex was more literary than personal, that she was more excited by Hemingway the writer than by Hemingway the man, that ambition rather than passion had inspired her marriage." The physical side of marriage, Rollyson writes elsewhere, "seemed 'the least important part of the relationship' to her. She had the best times with men who were her chums, 'chaps' who had no special claim on her."

A friend of mine who collects Hemingwayana recently allowed me a look at a sheaf of letters that came his way, written by Gellhorn from Sun Valley and from Cuba, in the early 1940s. These letters convince me much more readily than Rollyson's prose does that his subject is indeed what used to be called a hell of a dame. Since the letters are the property of their author, they cannot be quoted here, which is frustrating. Such frustrations, of which Rollyson must have had plenty, put no spring in a biographer's step. But if he seldom sounds inspired, he achieves an impressive portrait all the same, especially of his subject's childhood and her forebears. I salute him for his diligence and Gellhorn for her spirit of adventure, and I thank my stars that she never had eyes for anything or anyone I wanted. Her mother, I'm told by someone else who was born in St. Louis in the first decade of this century, used to say with a sigh that "Martha is a law unto herself." And so, it would seem, she still is. Jane Howard, author of "Margaret Mead: A Life," is at work on her fifth book, "Lost in the Interior," a personal account of the Midwest.