If, as Carl Sandburg suggested, a baby is God's opinion that the world should go on, what is one to make of Kerry Ryan, a child saddled with 22 serious birth defects? What Kerry's parents, Michael and Maureen Ryan of Stony Brook, N.Y., make of her is this: Kerry, they believe, is part of the wretched legacy of America's chemical war in Vietnam.

By now most Americans have heard about Agent Orange, a herbicide that U.S. airmen sprayed on forests in South Vietnam. The Vietnamese called the defoliated regions "the land of the dead" but U.S. Army manuals described Agent Orange as "relatively nontoxic to man or animals." Few American servicemen asked: Relative to what? The GIs handled the chemical rather cavalierly. On spraying missions they flew through clouds of herbicides without even wearing gas masks. Their slogan: "Only We Can Prevent Forests."

The chemical program was suspended in 1971 after the press reported that Vietnamese women from defoliated zones were giving birth to deformed children. Seven years later many American mothers, whose husbands had served in Vietnam, began noticing a similar pattern of cause and effect in this country.

Maureen Ryan was one of these women. Kerry, her only child, looked like a Thalidomide baby. She had a tiny, twisted arm and would never be able to walk. She had a severe heart defect and double sets of reproductive organs. And that was only for starters. For every flaw corrected by major surgery doctors discovered two new ones.

Until 1978, Maureen Ryan and her husband Michael, a policeman, blamed themselves for their daughter's misfortune. But then they read about a possible link between the defoliation program and health problems among American veterans and their offspring. Since Michael had been mildly exposed to Agent Orange in Vietnam, and had suffered unexplained illness afterwards, the Ryans naturally took a fresh look at Kerry's imperfections. Claiming that they had been "betrayed" by their country, the Ryans became activists in the veterans' movement. They charged that the Veterans Administration was not taking Agent Orange seriously. They spearheaded a class-action lawsuit, joined by several thousand vets, against chemical companies that manufactured the substance.

And now, with the help of Chicago journalist Clifford Linedecker, they have told their story in a book, "Kerry: Agent Orange and an American Family." Apparently this is a story whose time has come. In the past two years several books have examined the Agent Orange controversy in some detail but "Kerry," because it focuses on the tragic/heartwarming plight of a single family, is the first that may reach a mass audience; it has been selected as a Literary Guild alternate.

"Kerry" has all the elements of a tear-jerker but, happily, it does not live up to this potential. Linedecker's writing, for the most part, is terse and effective; even when he goes on and on, in gruesome detail, about Kerry's medical travails, you feel more numb than manipulated. When Kerry is taken to Lourdes to be cured, Linedecker does not make a big deal out of it. Kerry is a remarkably buoyant child. When Linedecker writes that her arm looks like a "chicken wing" you feel: If Kerry can take it, I can too.

For the reader who does not know a great deal about Agent Orange the book can be a helpful primer. It includes brief, accurate, well-composed historical appraisals of Dioxin, the use of herbicides in Vietnam, and Agent Orange's day in court. But while Linedecker's restraint keeps "Kerry" from being maudlin it also prevents it from being soul-searching or profound. Medical bills mount, frustration builds, but except for an occasional "Why me?" the Ryans rarely utter a discouraging word. Exactly one paragraph is devoted to a "low point" when their religious faith is shaken. When a doctor suggests that it might be better for the Ryans if their daughter passed away ("Why throw good money after bad?") Maureen is justifiably enraged--but did the same thought never occur to her?

The first half of "Kerry" is admirably dispassionate, but when the Ryans become absolutely convinced of Agent Orange's culpability Linedecker cheers them on. The whole tone of the book changes. Phrases like "our precious land, water and air" suddenly appear. Minds become "facile," determination is "dogged." Linedecker gushes over the Ryans' attorney. The book ends on a well-intentioned but pathetic note, with Linedecker making a telethon-style charity pitch aimed at the government: "Kerry Ryan is growing up. She outgrows a pair of $1,000 braces every year. She needs a lightweight, battery-powered wheelchair or Portacruiser."

Yet the message rings clear. Linedecker, the Ryans--and, the book indicates, Kerry herself--believe that Agent Orange should be regarded as guilty until proven innocent, not the reverse, which is the current official policy. I couldn't agree more. The burden of proof, in the case of Agent Orange and many other poisons, is unfairly distributed; people have to get sick or die to prove their point. As "Kerry" shows, this extra weight rests too heavily on individuals and families who have suffered enough.