What life-prolonging medical treatment do you want if you become hopelessly ill?

Nobody likes to think about it -- which is precisely why experts say you should. One way is by making a living will.

A living will is a statement to your family and doctor specifying what medical treatment you want -- or don't want -- if you become irreversibly injured or sick with no chance of regaining a meaningful life.

Over the past 12 years, 38 states and the District of Columbia have enacted living will laws. Though they vary from state to state, the common aim is to protect a patient's right to refuse medical treatment.

A living will declaration can be simple and brief. Here is the model statement, from the Uniform Rights of the Terminally Ill Act:

"If I should have an incurable or irreversible condition that will cause my death within a relatively short time, and I am no longer able to make decisions regarding my medical treatment, I direct my attending physician . . . to withhold or withdraw treatment that only prolongs the process of dying and is not necessary to my comfort or to alleviate pain."

Beyond that, it can specify particular medical procedures and designate an individual as a "proxy" to make medical decisions on the patient's behalf if necessary.

The statement must be signed, dated and witnessed by two adults. Copies should be given to one's family and physician.

Courts increasingly have recognized a patient's right to refuse treatments such as artificial respirators or feeding tubes, which can keep a person technically alive even when the body has stopped functioning normally. But when someone else has to make the decision on behalf of an incapacitated patient, a living will -- even in states without living will laws -- may provide the clearest evidence of the patient's wishes.

Some experts recommend a stronger form of protection: durable power of attorney. Ordinary power of attorney -- authorizing another person to make decisions on your behalf -- lapses if you become incompetent. A durable power of attorney continues.

The "Handbook of Living Will Laws" is available for $8 from the Society for the Right to Die, 250 W. 57th St., New York, N.Y. 10107; (212) 246-6973.