THE CRUZAN case, decided by the Supreme Court on Monday, does not stand for the proposition that people in a persistent vegetative state must be kept alive indefinitely by artificial feeding. The question decided was simply whether the United States Constitution prohibits a state, in this case Missouri, from requiring that those acting on behalf of the patient show clear and convincing evidence that their decisions are consistent with hers. Though the ruling is certainly a blow to Nancy Cruzan's devoted and long-suffering family, the Missouri legislature can change the result. And individual citizens, whether in Missouri or elsewhere, who are appalled at the prospect of being kept alive in a coma for years, can take steps to see that this does not happen to them.

A generation ago, a situation like Nancy Cruzan's was unthinkable. In 1983, when she was only 25, the young woman was in an automobile accident and her brain was deprived of oxygen for about 15 minutes. She has been in either a coma or a persistent vegetative state -- she exhibits certain motor reflexes but no cognitive function -- ever since, kept alive by artificial feeding and cared for in a state hospital at public expense. There are about 10,000 others in similar situations around the country. Until fairly recently, however, these patients could not have been fed by tube for more than a few weeks. Now, technology makes it possible to feed patients this way indefinitely. But what is possible is not always wise.

If the patient were terminally ill but competent, she could refuse medical treatment. If she had left a living will, her wishes would have been carried out. If she had given some family member a durable power of attorney, that person could have acted in her behalf. But because she was young and in good health when tragedy struck, it is not surprising that Nancy Cruzan had never taken these steps. Even then, the Missouri statute would have allowed her parents to act in her behalf if she had made her intentions clear in a less formal way. The courts found, though, that some remarks made to a housemate did not meet this standard, and that the Missouri law, while not necessarily desirable, is not unconstitutional.

Last winter, the Missouri legislature considered revising the state law to allow three doctors and all the immediate family members to make decisions for an incompetent patient. The change was not adopted, and it must now be reconsidered. Sensible models can also be found in other states -- Illinois, Connecticut, California and Minnesota were specifically cited by the Supreme Court majority -- that give greater authority to those acting in a patient's behalf. And individuals can take steps to make living wills or give durable powers of attorney to a friend or relative. This is a difficult area filled with emotion and conflicting views about rights, responsibilities and common sense. The Supreme Court's decision to move slowly and encourage the states to act is not unreasonable.