AT CHRISTMAS TIME, 1967, when my family went to visit my grandmother at the Boston University Medical Center, the doctors took my father aside and told him that she did not have much longer to live; the cancer for which they had just operated was spreading. About 20 operations and over five years of determined suffering later, she is still fighting the disease that should have killed her long ago.

Physicians in hospitals in Boston and Washington who have treated her are amazed that she has lived so long with the cancer engulfing almost all her internal organs, most of which have been wholly or partially removed. Throughout her bout with the disease, the doctors have maintained that she does not have much longer to live. But cancer, like other afflictions for which we have no cure, can be very unpredictable.

The question of precisely when a patient suffering from a so-called "terminal" disease is beyond hope of recovery is a highly subjective one and one with which doctors have a great deal of difficulty. It is, for this reason, one of the funademental problems involved in euthanasia.

EUTHANASIA--literally "good death"--involves either the direct mercy killing (active euthanasia) or the more common practice of withholding lifesaving drugs or treatment (passive euthanasia) from patients deemed to be in extreme suffering and without hope of recovery.

The questions raised by euthanasia, especially active euthanasia, are profound moral ones, and for the most part remain unanswered. One thing is for sure: To date most of the burden of decision remains in the hands of individual doctors. At this time there are no national or state guidelines to outline just how to handle cases which may involve some form of euthanasia, and few hospitals have advisory groups to help doctors resolve the ethical and legal problems they may face.

Mercy killing is illegal in most countries: in a recent trial in the Netherlands, for example, a famous physician was found guilty in the mercy killing of her terminally ill mother. This, however, brought forward a large number of doctors who admitted that they had induced painless death in patients who preferred to die rather than to continue suffering. Although most doctors in the United States say they will not perform actual mercy killings under any circumstances, some favor such a practice if the patient, family and attending physicians conclude that it is the most "humane" solution.

The frightening fact is that if mercy killings are performed--and undoubtedly some are--the incidents can easily remain a secret between the attending doctor and the family, or even just the secret of the doctor. The death of a patient already diagnosed as hopeless would neither surprise nor arouse suspicion in anyone.

All of the physicians and legal experts with whom I talked said that they were opposed to any use of active euthanasia, and for the most part they reflected the mood of doctors and legislators throughout the country. Mercy killings involve the basic moral question of whether anyone ever has the right to take another person's life. And the possibilities for abuse or extreme extension of the right to put people out of their misery, either by individuals or governments, are far too obvious for people living only 30 years after Hitler to accept. While the courts have dealt more lightly with mercy killers than with murderers, it is unlikely that active euthanasia will become accepted practice in this country in the near future.

PASSIVE EUTHANASIA is not considered murder by the U.S. legal system and in fact is practiced every day in hospitals all over the country. Usually it involves withholding drugs, treatments or heroic measures which, in the opinion of the doctor and the patient's family, merely prolong suffering and the patient's inevitable death.

A recent survey conducted by Louis Harris concluded that Americans are opposed by a 53 to 37 per cent margin to the practice whereby "a patient who is terminally ill" should have the option to "tell his doctor to put him out of his misery." Harris also said, however, that 62 per cent believe that a patient with a terminal disease "ought to be able to tell his doctor to let him die rather than extend his life when no cure is in sight."

The three main reasons cited by opponents of active euthanasia in Harris sampling were:

* "Death should be left to God or to nature and should not be controlled by man";

* Such a practice "puts too much of a burden" on the doctor involved in the case, forcing him "to play God"; and,

* Mercy killing is "just plain murder and that is wrong."

Those who favored mercy killings justified them mainly by reasoning that "it is the patient's life, and the choice should be left up to him." Others said that "anyone is entitled to put a halt to suffering that can only end in death anyway."