"Mercy killing," the intentional but well-meaning taking of a human life, is against the law in every state of the union and throughout the world.

The American Medical Association in 1973 adopted a policy-which is in turn followed by the Medical Society of the District of Columbia-which states:

"The intentional termination of the life of one human being by another [mercy killing] is contrary to that for which the medical profession stands and is contrary to the policy of the AMA.

"The cessation of the employment of extraordinary means to prolong the life of the body when there is irrefutable evidence that biological death is imminent is the decision of the patient and or his immediate family," the statement continues. "The advice and judgement of the physician should be freely available to the patient and his immediate family."

Physicians have turned off life sustaining respirators for the roughly two decades the respirator has been in general hospital use, deciding in each case, on an individual basis, that the support provided by the machine is no longer appropriate medical treatment for the particular patient.

These decision, said Frank Ferraraccio, executive director of the Medical Society of the District of Columbia, are reached after consultation with specialists, the patient where possible, and family members. "I'm not really sure how common it is," he said. "You keep hearing stories, but it's a private affairs."

The known facts in the Stephens case-the patient's terminal cancer, repeated heart failure, pneumonia and coma-appear to place it in that category in which physicians frequently decide to cease treatment.

What makes the case unique in the District is the fact that the patient's daughter, rather than a physician, physically disconnected the respirator.

"I don't think one would want to condone the general practice of having relatives disconnect life support systems," said Leroy Walters, director of the Center for Bioethics for the Kennedy Institute of Ethics, at Georgetown University.

"Since it's so difficult to determine motives, one wouldn't want to open the doors . . . because some people might want to hasten the death" of a relative for less than honorable reasons, he said.