WHAT IS the definition of death in a time when machinery can keep hearts pumping involuntarily and when quick medical attention after an accident can leave one part of the brain dead and another alive? In 23 states and the District, a dead person is one whose heart has stopped beating. In the other 27 states, including Virginia and Maryland, there are varying degrees of recognition that when the brain or part of the brain stops functioning, death can legally be pronounced. This hodgepodge means that a person can be legally alive in one state and dead in another. It distorts physicians' decisions because of the fear of lawsuits. It frequently leaves doctors and families at a loss to determine when attempts at keeping a person alive should stop.

District city council member Polly Shackleton has now gained council approval for a new definition of death in this city: complete loss of brain functions or--along the lines of the traditional definition of death--stoppage of the heart and lungs. In a parallel effort, the President's Commission for the Study of Ethical Problems in Medicine and Biomedical Behavioral Research recommended in July that Congress legislate a national definition: "irreversible cessation of circulatory and respiratory functions or irreversible cessation of all functions of the entire brain, including the brain stem. . . ." That proposal has been endorsed by the American Medical Association and American Bar Association.

The commission's definition requires no triggering mechanism to come into effect. But the District's definition would come into effect only when a person had signed an affidavit accepting it in the presence of two witnesses, and when two doctors had certified that the affected person was suffering a terminal condition. Until then it would not be legally possible for the person to avoid being kept alive by machine.

These measures represent compassionate attempts to deal with a dilemma created by modern medical technology. Despite the concern of the Most Rev. James Hickey, Catholic archbishop of Washington, that the Shackleton bill might contribute to the "declining respect for human life," neither that measure nor the commission proposal allows doctors or families to make decisions ending a life on the basis of their own whim or convenience. But the differences between them are important.

The commission proposal is preferable. It sets a nationwide standard. And it would apply to all citizens, not only to the relatively few who would have signed a legal document earlier. With the Shackleton proposal, doctors and families could end up in an even more precarious legal position: how would they act for a person who had not signed? The intent of legislation in this area is to diminish ambiguity, not increase it. The national proposal does that better than the local one.

The question remains: if one believes that the government should not be in the business of determining when life begins, why should it have a say in when life ends? That would seem the height of intrusion. But neither proposal attempts to constrain an individual or a family that may want to do everything possible to save a life. A government standard as proposed would broaden the realm of choice for individuals and families in the anguishing circumstances created by modern medicine.