WITH THE 50th anniversary of the publication of Gone With the Wind upon us, southern novelist Rita Mae Brown, author of the underground best seller Rubyfruit Jungle and other outr'e contemporary works, has turned her considerable if uneven talents to a Civil War novel set in and around Charlottesville, Virginia, where she now lives.

The story opens on the eve of Fort Sumter at the Chatfield plantation. Mother Lutie, driven half-mad by her husband's infidelities, sees ghosts, talks to a familiar named Emil, and dreams of a bat who wears ruby earrings and sings Mozart. Below stairs, a slave named Auntie Sin-Sin provides a restrained Virginia version of the voodoo element, while a younger maid, Di-Peachy, has light skin, hazel eyes, and breasts that "stuck straight out like hard melons." The men of the household are the silver-haired master, Henley, who breeds horses and may have fathered Di-Peachy; and son Sumner, a Tarleton-twin type well on the way to useless but endearing cavalierhood.

What the Chatfields do not have is a resident belle. Daughter Geneva is six feet tall and so skinny she could wash in a gun barrel. Horse-crazed, she is seldom out of the saddle and, although 18, hardly ever menstruates. The last is of some concern, for the eve of Fort Sumter is also her wedding day.

She marries Nash Hart, who is slim, blond, sensitive, and intellectual -- and if that isn't Ashley enough for you, consider what happens to him on his wedding night: "She grabbed him. She was strong and squeezed the breath out of him." Despite the role-reversal, Nash performs his husbandly duties so well that Geneva cannot bear to be parted from him when he goes off to war, so she cuts her hair, dons men's clothes, and follows him to Harper's Ferry, where she joins the First Virginia Cavalry and fights by his side at the battle of Manassas under the command of Major Mars (!) Vickers, who is not blond, not slim, not sensitive, and not intellectual, but who "reeked of masculinity."

BESIDES COPING with the spectacle of Rhett Butler in a menstruation-free tomboy heaven, we must also cope with Brown's literary style. Whether from a tin chronological ear or carelessness or both, she puts jarringly modern phrases into the mouths of her 19th- century characters and into her own exposition: don't waffle, didn't know beans about, what's the big idea?, a pain the ass, she chewed her out, and "navy" blue -- surely not a color term at this time. Even more unsettling than any of the foregoing is "Jesus H. Christ," an oath that, to the best of my recollection, first saw the light of print in a John O'Hara novel.

She uses pretentious words like "noctilucent" and "hellacious" and strains for metaphors: "Dawn licked the mountains," and "Gray fingers grasped the night, slowly, tearing it into day." Worse, she doesn't strain for metaphors, as in the sex scene when she has Nash reflect: "He thought he died and went to heaven." Her grammar is shaky: "bid" for "bade" and "snuck" for "sneaked." The title of a Shakespearean play used for a password emerges as "love's labor lost" instead of "Love's Labours Lost," and her research sticks out, as when Henley checks into "the Spotswood Hotel at the southeast corner of Eighth and Main Streets in Richmond."

This is one of those books that start getting good just when the reader is about to throw them across the room. Once Brown leaves Geneva to her adolescent sex-change fantasies and turns to other characters and events, she finds her stride and gives us a vivid and soul-searing picture of the psychological effects of war on decent and intelligent human beings.

Her finest moment comes in a train depot scene when a mother who has volunteered for nursing work opens a coffin and finds the body of her son. Rejecting the often irritating fastidiousness of Margaret Mitchell, Brown writes: "What was left of Greer Fitzgerald was in three pieces. His head was separated from the torso, which clearly wasn't his since it was clothed in a Yankee tunic. The legs, however, were clad in Confederate cavalry pants that had been proudly sewn by his mother. . . . she put down the lantern beside the coffin, reached in, and picked up Greer's head. . . . If anyone tried to get close to her, she backed off, tightly clutching her son's head. . . . When Hazel attempted to get the head from her, Jennifer snarled and then tried to bite her son's head. She was actually trying to eat him."

She does a splendid job on behind-the- scenes power struggles in the Confederate bureaucracy, and proves that she can weave her research into her story when she makes, effortlessly, the interesting and heretofore ignored point that, as a brand-new nation, the Confederacy had no party out of power to force the government into a more balanced stand.

She also proves that she can turn a phrase. Brushing the flies away from the corpses of the soldiers, the grieving mother "noticed as she squashed one that it smelled like the rotted flesh it had been eating," while an expert rider mounting a horse "sprang on the animal like a cricket."

As with Dickens, Brown's minor characters are better than her major ones. She creates a perfect good ol' boy in Banjo Cracker, a rough diamond who helps Lutie recover from the death of her son. She de- canonizes General J.E.B. Stuart and turns him into an interestingly flawed human being instead of the unrelievedly gallant beau sabreur other writers have made him. She captures with underwritten subtlety the dumb misery of unrequited love in the slave Big Muler, and she paints an accurate psychological portrait of the interior struggles of a woman who is far too intelligent to be a southern belle, but who tries to be one anyway.

Brown also knows her Virginia and the many ways in which the Old Dominion was and still is different from the magnolia- drenched Deep South. Her story contains no hotheads who surge off to war in ruffled shirts and armed with nothing but dueling pistols; except for the ridiculous Geneva, who carries on like Frank Yerby's Etienne Fox, the characters manifest the rationalism and restraint of a people whose values were formed in the 18th- rather than the 19th-century.

Stick with this novel, it will grow on you. Brown's stylistic faults are the kind that can be easily corrected in future works; meanwhile, she has proved that she can make the jump to a new genre. That in itself is rare and commendable.