RICH IN LOVE By Josephine Humphreys Viking. 265 pp. $16.95

A GOOD NOVEL exists in its own time, makes its own self-contained world. For the writer of serious fiction, the topicality that strains toward trendiness is therefore a risky proposition. Taken too often to the K-mart, the reader may awaken from the fictional dream, may look around with a cold eye and ask rudely: Is that the way things really are? We do not question the human truth of Tolstoy's "Happy families are all alike, but an unhappy family is unhappy in its own way." But we lose some of our trust in what is being related to us when we come upon a sentence like "All around me I saw the American family blowing apart, as described in Psychology Today," an assertion made by Lucille Odum, the 17-year-old narrator of Rich in Love. The reference is so current that the statement seems curiously passe'. "Hey, wait a minute," we think. "When was that Psychology Today article published?"

Like Dreams of Sleep, Josephine Humphreys' second novel, Rich in Love, is set in the New South in a landscape rapidly losing its character and history to bulldozers and shopping malls. In this very real setting, she has placed the Odums, her fragmenting American family, giving us not realism but a kind of fairy tale. Peopled with almost obligatorily eccentric characters, Rich in Love is winning and touching at times, but the spell Humphreys attempts to cast over the reader is undermined throughout by forced relevance, forced "wisdom."

It's the story of what happens to Lucille Odum, Humphreys' unawakened sleeping-beauty heroine, after her mother, 49-year-old Helen, abruptly abandons the family one day, leaving a bag of groceries and her pocketbook in the car and leaving the already spinsterish Lucille with too much responsibility. What runaway wife would leave her pocketbook behind? one might ask, though in other ways Helen's flight is reminiscent of the old "run-away-wife-in-search-of-fulfillment" phenomenon of the 1970s. Clearly Helen Odum is having a colossal mid-life crisis; clearly the daughter will have to go in search of the missing mother.

Lucille Odum is special, we learn very early on, set apart, like some heroine of romantic fiction. She was born with a harelip; all that remains of it by her 17th year is a tiny white scar, though that scar looms large within her consciousness. She was Helen's unwanted second child; in fact she has learned that her life was saved by the inefficiency of the suction method, which aborted her twin but left Lucille inside her mother undetected and relatively intact. The missing twin is another thing that makes Lucille feel odd, incomplete. What she has been blessed with is a surplus of intelligence and intuition -- almost more intelligence and intuition than this novel can bear.

It's not just that Lucille is one of those kids who's a precocious reader (everything from Virgil to Psychology Today) even though she's dropped out of high school to take care of her grief-stricken 60-year-old father. It's that Josephine Humphreys has made her so incredibly all-knowing. Lucille Odum knows more about life than a 45-year-old woman, despite her youth and staid middle-class upbringing in a Charleston suburb. Unfortunately, no one is more aware of this than Lucille herself. "I see lots of things no one else sees," she rather smugly tells her would-be boyfriend, Wayne.

Sometimes she is authentically prescient, and her narrator's voice is right on the mark: "I was regarded as an abstainer in every respect, a good girl. But I felt the pang now and then. People like me are sometimes hanging onto their so-called goodness by a thread." When her older sister Rae turns up on the doorstep very pregnant and introduces Lucille to her brand-new husband, Billy McQueen, Lucille makes the delicious observation that "a new husband is like a squatter. You can't run him off your property, he is there for good."

Other times, however, the reader feels assaulted by Lucille's deep perceptions -- always presented in the most authoritative cadences, never with a touch of self-irony. Lucille looks at her father and thinks: "The sorrow of a big man is worse than that of a small man, rocks him deeper, lasts a longer time." This has the ring of an eternal verity, but is it really necessarily true of big men? And who is really addressing the reader at such moments -- the character or the author, having her own say, indulging herself with yet another graceful sentence?

Although immersed in her own sorrows, Lucille constantly reminds us that the American family is not the only thing blowing apart. She worries earnestly and vocally down a checklist of current issues: the Greenhouse Effect, the nuclear submarines in the harbor, the urbanization of the environment. The novel is so relentlessly up-to-date that Billy McQueen reveals to Lucille that he has deliberately impregnated Rae by punching holes in a series of condoms.

Of course, Lucille has her sexual awakening -- only halfway with Wayne, then much more thoroughly with her dangerously depressed sister's husband. They make love on Halloween as Rae gives birth upstairs into a toilet. "Tragedy, well-known for its convoluted methods, reunited the family."

When we last see Lucille, she is holding baby Phoebe on her lap and being profound one more time: "What I want her to know is the strength and fragility of things, the love and the luck hidden together in the world. How to say so is hard. We ride farther and farther to get a view; we forget more and more what ought to be remembered. But she is like me, and she will know."

And what do we learn from all this? Motherhood triumphs over all ambivalence? Nothing can replace the nuclear family but a less closely linked family of fragments in separate households? Once " 'Family' meant people in a house together. But that was in a language so far back that all its words are gone, a language we can only imagine." Somehow Humphreys intends this to be optimistic though hardheaded wisdom for our troubled times, but in the context in which it is presented it is only an expression of the New Sentimentality.

Joyce Johnson is the author of "Minor Characters" and co-winner of the first prize in the 1987 O. Henry Awards.