The Road From There to Here : ROADWALKERS, <i> By Shirley Ann Grau (Alfred A. Knopf: $22; 272 pp.)</i>

Pulitzer Prize-winner Shirley Ann Grau’s ninth work of fiction begins promisingly as a sweeping social novel in the no-longer-fashionable fashion of John Steinbeck:

“In 1934 this is the way it was. Homeless people were moving in a steady flow across the southern part of the country, back and forth across the surface of the earth, seaweed on a tide that ebbed and rose according to seasons, following rumors and hopes, propelled from place to place by police and sheriffs and farmers with shotguns, and closed doors and locked gates. . . . They were called roadwalkers.�

Early on in her nearly 40-year career as a writer, Grau established a reputation for leavening her expertise regarding debutante New Orleans with an uncondescending view of the South’s poorer black and white residents. In this book she quickly zeros in on a small stunted black child known only as Baby. Baby begins life as one of six siblings in a small-town family “with four pecan trees in the yard.� But in a flash all she has vanishes. Around the time she is born, her father deserts the family for another woman. Her mother departs shortly thereafter. The children find Aunt Rosie in a nearby town, but Rosie, overwhelmed, practices a heartless triage, abandoning Baby with two of her siblings by the side of the road when she heads off with the other children toward a relative who works as a Pullman porter in Atlanta. In a few short, blameless years, Baby has sunk to being a roadwalker.

With her brother Joseph as her tutor, Baby drifts from town to farm. They steal eggs from henhouses and milk from unwatched cows. Here Baby’s tiny size is a virtue: “What she could do was this: she could wriggle through the least crack in a fence or window and open it wide for them to come back to later.� These pages, which chronicle Baby’s feral existence, her constant exposure to disease and fear of a shotgun blast, are beautifully imagined and written. But soon “Roadwalkers� loses its footing and begins to feel like an oddly matched set of novellas joined along exposed seams.

Baby is “captured� by the employees of an idealistic plantation owner, who sends her, mute and barely housebroken, to a school run by nuns. There she is considered a hopelessly wild child until she demonstrates an unsuspected talent for drawing bright, evocative religious images. Re-christened Mary Woods by the nuns, Baby is enraptured by African gods invisible to her Christian handlers.

Then “Roadwalkers� shifts abruptly now into the first person, becoming the account of Nanda Woods, Mary’s daughter, who at 36 years of age narrates her childhood retrospectively. Much has changed in the interim: Mary has become a successful New Orleans couturier. Nanda is her model, and the two are famous enough to be featured in Newsweek (this strange turn of events is actually an expansion of Grau’s short story, “The Beginning,� from her last book, “Nine Stories�). Nanda faces the challenge of integrating an eastern Catholic boarding school.

For a novel that has begun with the grand impersonality of “The Grapes of Wrath� to reach suddenly for the autobiographical intensity of Lorene Cary’s “Black Ice� or Jill Nelson’s “Volunteer Slavery� is tricky enough. But Nanda, drawn as a thoroughly whiny and ungiving young woman with resentment as deep in her blood as art was in her mother’s, makes this improbable retooling yet harder.

Though Nanda excels academically, she despises the tokenism which has brought her to this nameless, prestigious school. She acts this anger out through minor mischief from experimenting with bisexuality to rejecting those who accept her. Ultimately she graduates from college with an attitude problem and a Phi Beta Kappa key. . . . Fast forward again as she finds in a young black doctor with an anarchic streak--an ideal groom for an open marriage. The time scheme of the novel now seems to have reached the swinging ‘60s. The novel concludes limply in the present with an epiphany from the adult Nanda: She and her husband “smile at each other, cautiously, warily, as we walk across the worm-infested lawn. . . . And so alone I came into my kingdom. My portion neither more nor less.�

Writing a novel is more like driving a train than a car--once it runs off the rails, recovery is rarely possible. “Roadwalkers� probably is doomed from the moment Baby is saved. But one wonders at Grau’s troubles with the latter part of the book. After all, she made her name in part through the expertise with which she brought alive women of Nanda’s age, albeit mostly white and rich women, like the manipulative Joan Mitchell in Grau’s wonderful “House on Coliseum Street� (published in 1961). Yet in “Roadwalkers,� the author’s first novel in 18 years, Grau appears to have lost access to the feel of young adulthood, which she once grasped so well.