DEATH USED TO BE the great equalizer. It was as inevitable as taxes, and awesome in its finality. Preparation for dying and what lay beyond preoccupied man and defined civilizations. But building pyramids, lighting eternal flames, and performing rituals, no matter how extravagant, could never alter an individual tragedy or the grim common destiny. One could resist death for a while, and with a little luck, choose where and when. But with few delays or complications, death always got its man. And when you were dead, you were dead. Those were the good old days.

Recent and anticipated technical advancements have whisked us to the threshold of an era of rebuilt humans, of makeshift immortality. Transplants and artificial organs may distort distinctions between man and his fellow man, and man and machine. Suspended animation may create real-life Rip van Winkles. Doctors have already agonized over choices of who to let live. While a poor man formerly had the consolation of knowing his employer couldn't "take it with him," expensive innovations may some day permit a wealthy man to live indefinitely.

Speculation about the far-out possibilities of science have always raised fascinating social implications. The new feeling is that so many of the obstables to what once was science fiction are now merely technical problems that will be solved in time. The everyday hygenics that have advanced the average lifespan 30 years in the last century pale beside the new methods of postponing death. Surgeons make daily use of ceramic and metal bones, synthetic arteries and electronic blood pressure regulators and bladder stimulators. Miraculous innovations that quickly have become almost commonplace suggest the great issudes medical ethics will be confronted with in the near future.

THE ABORTION ISSUE has focused on a definition for the beginning of life. When transplants are performed on the same scale, an adequate definition of death will become just as controversial. The traditional termination of spontaneous heartbeat and breathing simply is not satisfactory. Emergency techniques have brought back many such clinically "dead." At the other extreme is the guideline of a cautious Dr. Maze, who wrote in 1890 that the first signs of decay should precede burial. For transplant purposes, this caution is a little restrictive.

Doctors searching for a workable definition have had to protect themselves from lawsuits and murder charges as well as protect the patient from the scalpels of overzealous transplant surgeons. Usually, they have called in an outside, objective judge: the electroencephalograph (EEG). The EEG measures electrical activity in the brain, which has displaced the heart as the recognized center of individuality. Cessation of that electrical activity is "death."

Unfortunately, the brain, which is damaged irreversibly within three to six minutes without oxygenated blood, does not always die at once. If the lower brain, which controls breathing, dies first, artificial breathing measures must be implemented to keep the organs in condition for transplantation. This may permit the rest of the brain to die slowly, even over a period of years. Perhaps the most expedient standard would be EEG readings showing irreversible damage, but few would have the courage to follow Aristotle Onassis's example of a few months ago in "pulling the plug" on a machine maintaining the heartbeat of an only son.

Infinitely more painful for the physician than denying a coma-stricken patient a vegetable existence is telling an outwardly active one that he cannot afford to live. Artificial kidney machines have proved the first example of a lifesaving treatment whose staggering cost had prevented widespread use. Sessions are long and painful, and the relief is only temporary, but for those who have had their kidneys destroyed by disease, it is the only alternative to a transplantation or death. Before adequate Federal funding was available, doctors in the field had to decide who would be one of the thousands to die yearly because they could not secure regular treatments.

These decisions are more brutal than those of a medic in combat, who must quickly decide who to treat on the basis of chances for recovery. Doctors frequently call for some broad standard to help them make these choices, but any guidelines turn out to be callous and dehumanizing. Who do you save, a father of four or a brilliant scientist? And what if a patient expresses a desire to die: is a cooperative doctor aiding a suicide? Disagreement with the patient, relatives and colleagues forces the physician to make these decisions alone and stand by them. In the absence of sufficient funding or any other guidelines, it is often reduced to a matter of who can afford the treatments.

IN THE LAST few years there have been an estimated 5000 transplants of kidneys, 1000 livers, 25 of lungs and 160 of hearts. Once techniques are perfected and the body's tendency to reject foreign objects is overcome, the practice will become much more common. Some doctors estimate that eventually one third of all humans will undergo a transplant at some point in their lives.

There is no shortage of corpses--2 million Americans die annually--and when a 1968 Gallup Poll asked respondents if they would be willing to donate all or part of themselves to medical science, 70 per cent said they would. This generosity is rarely translated into legal steps, however, as reflected by the current cadaver crisis in medical schools.

The pool of potential donors is reduced even more by the nature of transplants. The only hearts that are usable come from victims of sudden accidents. It takes only 20 to 30 minutes without circulation to damage the heart--precious time when the organ is being rushed to a specialized operating room and a suitable patient. Organ banks will only make the shortage of donors more dramatic, and hospital wards will continue to be filled by cardiac patients hoping for the extraordinarily good luck of a healthy stranger running into extraordinarily bad luck nearby.

This raises the prospect of a new breed of ambulance chasers, prepared to make quick payoffs to secure organs for ailing clients. Already many people carry cards permitting use of some or all of their organs after death.

A whole new set of psychological responses in transplant cases are being studied. The recipient is so unique he does not even know how he is expected to react. The heart is the most palpable of organs: How does it feel to have a dead man's pulse? The easy response is any pulse is better than none. But surely there are lonely hours when an organ recipient realizes that he is no longer totally the same man.

Of course, the donor need not always die, and the organ need not be as evocative as the heart. The kidney operates silently, and there is a large pool of potential donors because most people have two. The donor of a kidney must balance the risk to himself against the reward of saving a life. For the purposes of tissue matching, relatives are preferred as donors. Often their motivation is more guilt than compassion, guilt that can blossom into resentment when all attention is focused on the recovering recipient. Once donors become a significantly large group, a whole new sort of therapy will have to be devised.

EVEN LESS PREDICTABLE are the implications of suspended animation. Although the art of cryogenic freezing is still crude, there are some reports of whole human bodies being preserved in the hopes of revival when a cure is found for a currently fatal disease. But current laws demand that the preserved patient be thoroughly dead before preservation and current methods of freezing cause so much cell damage that the process along is probably fatal.