By Lincoln Caplan

Farrar, Straus & Giroux. 151 pp. $17.95

To nonbelligerents, the furious squabble over "open" vs. "conventional" adoption may seem one of the most inexplicably vituperative -- if not outright fatuous -- disputes in modern memory.

Americans adopt 3,000 kids a week. Two-thirds go to relatives or stepparents; only about one in five fits the familiar image of an infant obtained by an unrelated couple, usually through an agency or attorney. Of those, most are "conventional" -- that is, the identities of the birth parents and adopters are kept confidential. But a growing fraction are "open" arrangements in which both parties know each other and may even cooperate to some degree in rearing the child. Each method has advantages for different circumstances, and you'd think the manifold diversity of American society could somehow accommodate both.

Yet it is almost impossible to find an evenhanded treatment of this issue because the best-informed sources are often yowlingly tendentious. That's what makes this compact work by Lincoln Caplan (an adoptive father and staff writer at the New Yorker, where much of the book appeared) so valuable. As he chronicles one recent adoption, interspersing the narrative with chapters on history and theory, Caplan manages to make his pro-open sympathies plain while arguing convincingly against prohibiting either approach.

Which isn't easy, since the adoption he chooses to describe is so open it makes the Grand Canyon look like a mail slot. The story begins in late 1987 when the girl Caplan calls Peggy, a 20-year-old junior at the University of Delaware, finds herself pregnant by her boyfriend "Tom," 22. Neither wants to get married. "They both planned to start careers, make some money, have fun." Seven months later, it's getting hard for Peggy to keep hiding her condition from her "baby-crazy" parents, and while grazing the want ads one day, she comes upon a listing by a "happily married, financially secure couple" looking for an infant.

The ad has actually been placed by a California attorney on the collective behalf of six eager couples, including "Dan and Lee Stone" -- a botany professor and nurse, respectively, in their late thirties and living near Boston. After four years of marriage and three miscarriages, they are nervously prepared to adopt. They needn't have worried: Peggy appears to have peeled herself right off the front of a Boynton greeting card. Playful, chipper, self-possessed, she has an uncanny clarity of vision. She doesn't believe the child is "meant" for her: "It was like a package delivered to the wrong address"; and giving it up "was like donating a kidney to another person."

After a brief initial meeting, Peggy travels to Boston to stay with friends of the Stones before giving birth. To be sure, there are irritations: Peggy needs more money and dislikes the social worker assigned to her; the Stones have intermittent seizures of doubt and remorse. When Peggy insists that the child be handed to Lee as soon as it's born "because she wanted the baby's first smell to be of its mother," Lee says, "I had this image of taking a kitten from its mother, and I thought of how horrible that is."

Nonetheless, their intimacy and affection grow. Even when the Stones poke a home video camera in her face, Peggy says, "You're giving me a lifetime of security knowing that my baby is going to be taken care of by its parents. I mean, what else can I ask for?" ("She's definitely not from Earth," says a friend of Lee's.) Finally, the Stones assist at the birth of little Rebecca and have their pictures taken minutes afterward, drinking champagne from Dixie cups. Peggy returns to Delaware, secure in the assurance that she will be a permanent part of an "extended family."

Conservative temperaments regard such relationships as more than a little creepy. But not knowing one's birth parents, open-adoption advocates insist, is worse -- producing a sense of "genealogical bewilderment" and dislocation. "The feeling of some adoptees," Caplan explains, "is that they do not belong anywhere, or that they belong somewhere other than where they are." Many experts believe this can lead to "adopted child syndrome," a conflux of educational and behavioral problems. (Research on this "syndrome" is far from conclusive.) Such kids, Caplan writes, can grow up "frustrated at not knowing their biological roots and at being part of the only group of American adults who are prevented by law from acquiring information that others assume is their birthright," and "feel enslaved by a perverse system, treated like children long after they become adults." Traditional-adoption proponents reply that giving a child -- or even an adult -- this information merely adds a second burden of confusion to the existing sense of displacement.

Caplan, the author of previous volumes on the solicitor general's office and the insanity defense, lays out these and other issues with a brisk circumspection. His prose can sometimes get too study-hall stiff for this warm-blooded subject, and he is rarely interested in evoking the physical image or emotional condition of his principals. Some topics -- especially teenage pregnancy -- are rather hastily treated. In part, that's the price of packing so much context into such a small book, and it's no small achievement. The reader gets a dollop of anthropology (adoption in the South Pacific), a little American history (the "placing-out" system that helped people the West with waifs) and plenty of politics (particularly the chapter in which Caplan thoughtfully disentangles the issues of adoption and abortion, which President Bush has muddled by boosting the former as a substitute for the latter).

We also get a splendid overview of the social vectors that converged in the '70s and '80s to favor open adoption. Some are familiar: the rise in infertility and deferred childbearing among married couples, the waning opprobrium attached to "bastards" and "barren" women, the new interest in genetics and the deterministic side of the nature-nurture dichotomy. But some are plainly supply-side forces: "A generation ago, four out of five unmarried new mothers" chose adoption, Caplan writes. By 1986 "the number had fallen to one out of 25" (one of every eight single white birth mothers, and one out of every 100 single black birth mothers). As a result, couples wishing to adopt outnumber healthy infants by ratios as high as 40 to 1. In short, it's now a seller's market in which, not surprisingly, birth mothers and their agents have sizable influence.

But sociological ripeness is one thing; the stubbornly intractable human heart is quite another. Each adoption is absolutely unique, no matter how much we may yearn to codify and systematize the process. And as Caplan warns, "open adoption depends on the optimistic notion that people can handle unfamiliar, even unprecedented, relationships." So the reader is not utterly shocked to discover, at the end of the book, that even the heroically amenable Peggy can't cope: Apparently pregnant again, she freaks out, flees Wilmington with her tuition money and finally resurfaces, pronouncing the whole adoption a "nightmare." The account she gave Caplan, she now says, was "not based on reality."

Does this lurid, late-breaking outcome invalidate the book? Paradoxically, no. In fact, it serves to reinforce Caplan's implicit thesis: Until we know a great deal more about adoption, we restrict its forms at our peril. The reviewer is a writer and editor for The Post's Outlook section.