Final wishes, in the form of a written will, trust or grant of power of attorney, usually are not revealed or carried out until after a death. And that has sufficed.

Until lately.

Today, the newest and most hotly debated "advanced directives" address a more modern fear: that of a protracted and unnatural dying made possible by medical technology so advanced it can sustain biological function long after brain death has occurred.

Two chief weapons in the fight to maintain individual control over the manner of one's death -- the so-called "living will" and the less well-known "durable power of attorney" -- are gaining support, despite legal and ethical problems.

"Many of us," says Tish Sommers, a national advocate of the new measures, "fear prolonged dying more than death itself." Sommers, 70, a terminal cancer patient, states flatly, "I don't want to be kept alive when there is no longer a chance of recovery to the point when I can still function and when life still has meaning for me."

The living will movement, begun in 1968, drew impetus from the widely publicized 1976 Karen Ann Quinlan case in which a New Jersey father won the legal right to remove life-support devices from his comatose daughter. The case brought home in a dramatic way the power of medicine to delay death, seemingly indefinitely, without offering hope for recovery. Since then, 35 states (Maryland became the 35th earlier this month) and the District of Columbia have passed living will or 'right-to-die' laws, recognizing a patient's right to refuse medical treatment when dying. Standard language specificially proscribes the "application of life-sustaining procedures [which] would serve only to artificially prolong the dying process."

Living wills, argue supporters like Sommers, serve the interests of not just the dying but also their families, by "relieving the guilt of a relative who must make a decision."

Because that relative is often female (women are the surviving spouses 85 percent of the time and disproportionately care for the dying in institutions and at home), society's changing attitude toward dying has been called a "woman's issue."

Public support, however, is by no means unanimous. The National Right to Life Committee, for example, opposes the legislation as unnecessary and dangerous, particularly when pregnant women are not excluded. But according to recent Gallup and Harris surveys, 8 out of 10 Americans now believe terminally ill patients have the right to die by asking doctors to stop treatment.

And while there have been incidents of living wills not being honored, the medical establishment is showing signs of coming around. Stanford University Hospital in California now distributes living will forms to every patient admitted. According to Concern for Dying, the nonprofit New York group that authored the first model living will, a major New York teaching hospital also is preparing a written policy honoring living wills.

Courts also are showing a change in attitude, say some legal observers. To date, fear of liability has tended to prompt caregivers to choose treatment over nontreatment in cases that are not clear-cut. Recently, however, an Ohio court ruled a hospital could be held liable for assault and battery for treating a patient against his wishes.

Durable power of attorney, now written into law in all U.S. jurisdictions except the District of Columbia (where several bills are pending), permits an individual to assign decision-making powers, in the event of his or her incapacity, to any chosen person. A few states, including Sommers' home state of California, have written new provisions into the law to cover life-support decisions specifically.

Legal experts say it offers clear advantages over the living will in legal protection and versatility.

Barbara Mishkin, a private health law attorney and former deputy director of the President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behaviorial Research, explained some of these advantages to 200 predominantly female participants at a recent Washington conference, "Taking Charge of the End of Your Life."

"Durable power of attorney is just as good for protecting your right to have treatment as it is for protecting your right not to have treatment," said Mishkin. (Living wills are nearly always written to withhold treatment.) Unlike a living will, she said, durable power of attorney can also apply when an individual is not terminally ill but temporarily incapacitated. It also avoids the need to anticipate all the possible situations in which decisions might have to be made.

Living will legislation is fraught with other drawbacks, chief among them the lack of uniformity. One state's living will may not be recognized in another state.

"A living will," said Mishkin, "can't be written for a child or an incompetent adult, except in a few states. In some states, a living will is binding only if the patient has been told of his terminal condition . . . In some states, the living will must be reaffirmed periodically . . . In five states, the living will must be filed with the court."

There can also be difficulty in determining precisely at what point a living will applies.

Says Nancy Coleman, staff director for the American Bar Association's Commission on Legal Problems of the Elderly, "I was just with a 38-year-old friend who has cancer. She's verbal. She can make decisions, but it's not clear if she'll live beyond July. When does a living will kick in, so to speak? When she's comatose?"

Often legal questions are tied up with ethical ones, as in the debate on artificial feeding. Does feeding via a nasogastric tube or IV constitute medical care that can be withdrawn, or basic supportive care that cannot? What if feeding can be shown to be more burdensome than beneficial? To many, the very question is morally offensive. The National Right to Life Committee, for example, says spokesperson Jan Carroll, is adamantly opposed to "allowing people to be starved to death."

Notwithstanding this, the handful of courts that have looked at the question, said Mishkin, have found "no conceptual, legal, or ethical difference" between artificial feeding and artificial respiration, arguing both treatments can be withdrawn. Maryland's new law specifies that feeding cannot be withheld; most state laws leave the question open.

Still more troublesome potentially is the fear that widespread use of living wills could encourage the systematic rationing of health care to the elderly. "There has been a concern lurking around for years that somehow the right to die could be transformed into a duty to die by means of social pressure or economic pressure," concedes Daniel Callahan, director of the Hastings Center, a New York research organization that studies ethical questions of medicine and biology.

Sommers herself talks about the living will movement, in this respect, as a "two-edged sword."

The fear is not so far-fetched, say Callahan and others, citing England's common practice of denying kidney dialysis to those over the age of 55. Closer to home, the Reagan administration's new patient reimbursement formula -- using Diagnosis-Related Groups, or DRGs -- provides incentives to hospitals for limiting care.

"Physicians today are increasingly making treatment-stopping decisions without consulting the patient," claims Robert Veatch, professor of medical ethics at Georgetown University's Kennedy Institute of Ethics. Veatch, 46, who has a living will, argues, "Public consciousness is still focused on the patient who can't get treatment stopped, but that's a relatively rare problem today . . . By far the more dangerous situation today is when a physician assumes treatment is not in a patient's interest or that he or she would not want the treatment."

The best insurance against this and other potential abuses, agree right-to-die advocates, is public education: the need to face death squarely as a social and personal issue.

"The vineyard waits urgently to be tended," former senator Jacob Javits, 81, who suffers from amyotrophic lateral sclerosis, or Lou Gehrig's disease, told the conference audience. The right to die in dignity, he said, in the short breaths allowed by his portable respirator, is "profound . . . moral . . . essential."