THE KIDS NEXT DOOR; Sons and Daughters Who Kill Their Parents. By Greggory W. Morris. Morrow. 306 pp. $16.95; EVERYDAY DEATH; The Case of Bernadette Powell. By Ann Jones. Holt, Rinehart and Winston. 202 pp. $15.95.

WHEN SHOULD a society allow one of its citizens to act as judge, jury and executioner? The concept of "justifiable homicide" is intrinsic to the American system of criminal justice; known best under the unfortunate rubric of "self-defense," it is a right that predates the social contract, said by our courts to inhere in the law of nature. Until recently, it has excused killing only in circumstances of absolute extremity, where a person has no escape or other alternative to an imminent danger of death or severe injury.

When Bernhard Goetz opened fire on four youths in a New York subway earlier this year, significant public opinion condoned, if not approved, his act. He had the good fortune to find seemingly worthy victims -- street toughs with criminal backgrounds -- and many people, sensing some ironic, if not righteous power in the frontier justice that Goetz dispensed, cared little if he may have failed to fulfill traditional standards of self-defense. While other defenses to homicide have been eroded -- notably that of insanity, in the wake of the backlash against John Hinckley Jr.'s acquittal for attempting to kill President Reagan -- self-defense has gained a vogue paralleled only by that of its institutionalized kin, capital punishment. Surprisingly, its most vocal proponents are not traditional law-and-order advocates, but liberal social activists.

In The Kids Next Door, journalist Greggory W. Morris presents a series of case histories, based substantially on personal interviews, of youths who have killed one or both of their parents. The subject is inherently sensational, and Morris does little to assuage the feeling of guilty horror that comes from even opening this book. Although he purports to tackle such weighty issues as "society's failure to deal with abused and mentally ill children and with the unequal treatment juvenile offenders receive," these matters are relegated to conclusory asides. The real business at hand is the promotion of a vaguely defined "battered child defense," which would loosen the standards of self-defense to excuse killings in the absence of imminent danger of harm.

The cause is compelling, but even the most sympathetic of readers may blanch at the notion of forgiving some of the homicides described here. Morris' strategy is to shock the reader into allegiance; from an opening vignette about a child literally cooked to death in an oven, The Kids Next Door wallows in its violence, relying upon the reader's faintness of heart rather his or her firmness of mind.

Equally disconcerting is the manner in which Morris embraces his "kids" (one of whom was 34 when he killed, and almost all of whom were teenagers prosecuted as adults). Each is depicted with a forgiving eye, while their victims are ominously faceless, discounted as abusive and thus, it would seem, deserving of their fate. And what becomes truly chilling about The Kids Next Door is not the dire undercurrent of violence in the American family, not the terrible dilemma which battered children who fight back present for our courts, but Morris' apparent certainty that the killings he reports are not only legally justified, but morally appropriate.

MORRIS' "battered child defense" owes much to the acclaimed collection of case histories by Ann Jones, Women Who Kill. Jones' new book, Everyday Death, focuses on one woman who killed, Bernadette Powell, whose 1979 murder trial and subsequent appeals were a cause celbre for women's rights advocates. The Powell case is riddled with mystery: its only certainty is that on July 9, 1978, just after dawn, Bernadette Powell killed her ex-husband in a motel room near Ithaca, New York, with one shot from a .22-caliber revolver. Powell claimed that she had been kidnapped at gun-point. She was found guilty of second-degree murder, and received the minimum sentence allowed under New York law for this offense: 15 years to life in prison.

Jones' interest is not so much in parsing out the "true" facts of the Powell case as in challenging the adequacy of the adversarial trial system to perform this task. Her political subjectivity is well-advertised (criminal justice is said to be dispensed "within the terrible constraints of the legal brotherhood," and men who commit crimes are labeled "increasingly violent," while their female counterparts are merely "increasingly poor and desperate"); but there is no sense of agitprop. For Jones, criminal law has become immaterial to cases such as Powell's; she presents here the complex facets of a troubled woman that trial by jury cannot apprehened.

Everyday Death is intriguing less as an inquiry into the criminal justice system than as a record of a writer's coping with the failure of her material. It begins as an apparent paradigm of the "battered woman defense," with Powell exposing her wounded wrists to Jones and screaming, "You want to see my scars? Just look at that. Why don't you write about that?" But the evidence, Jones soon learns, is less than unequivocal; by the book's close, she is speculating about split personality in an effort to reconcile significant evidence of premeditated murder with the humane, sympathetic woman she believes she has come to know.

Both Everyday Death and The Kids Next Door argue for a kind of justice that moves beyond facts to sociological and psychological theories, taking an expansive look "at the whole context of an act." "To be effective," states the introduction to The Kids Next Door, "we must put the (victim's) behavior on trial also." This stance -- which has been properly rejected by most progressive jurisdictions in the equally volatile arena of rape prosecutions -- is, as are most attempts to engender social change via criminal law, a questionable ideal. Eradication of the horrors of family violence should be a national priority; but whether we -- and the judicial system that we have erected to regulate and discipline our behavior -- should countenance homicide in its name is another matter entirely.

The story of Bernadette Powell is no more one of "everyday death" than Greggory Morris' case histories are representative of "kids next door." No matter how worthy the underlying cause, to suggest that justifiable homicide is ordinary is not only wrong, but potentially dangerous. We need only note the testimony that Bernadette Powell had read a newspaper article about a woman who shot her husband and was sentenced to only one year in prison; Powell, we are told, said that she "was going to do the same thing . . . (and) get away with it."