VOTERS in Washington State have the chance tomorrow to break new ethical and professional ground for the practice of medicine.In considering a controversial ballot measure, they are pushing medical debate into a new frontier - beyond the issue of an individual's "right to die" to the question of whether physicians may officially aid their patients in committing suicide. Although some doctors in the Netherlands quietly engage in euthanasia without fear of prosecution, no Western nation has legalized the procedure. Many states are watching the outcome of Washington's Initiative 119 and considering similar measures. The European Community is about to take up the question for member nations. The question being put to voters here is straightforward: "Shall adult patients who are in a medically terminal condition be permitted to request and receive from a physician aid-in-dying?" The proposal amends the state's Natural Death Act of 1979, which provides for the withdrawal of medically life-sustaining procedures in cases determined to be terminal, to include "irreversible coma and persistent vegetative state." And it includes artificially administered nutrition and hydration among those procedures. More significantly, the measure also provides that mentally competent adult patients who are determined by two doctors to have no more than six months to live may be assisted by a doctor in taking their own lives in a "dignified, painless, and humane manner." No one but the patient could make this decision, which would have to be witnessed by two impartial persons, and no physician would be forced to carry out such a step. The procedure to be used is not specified. Supporters stress that the proposal includes many safeguards against abuse, and that the issue is one of personal choice. The ballot measure "offers choices to terminally ill patients, choices which today can be made by doctors or hospitals, and even by judges, but not by the patients themselves," says Seattle family doctor Linda Gromko. "It's not a decision that can be made by anybody else - not the family or the doctor," adds Shannon Braddock of Washington Citizens for Death With Dignity. "And obviously you can change your mind at any time." Opponents, including the Washington State Medical Association, say the proposal directly contradicts a key tenet of the Hippocratic Oath sworn to by physicians: "I will neither give a deadly drug to anybody if asked for it, nor will I make a suggestion to this effect." Rather than encouraging aid and comfort for suffering patients, says State Rep. John Moyer (who is also a physician), Initiative 119 "provides us with an easy out when end-stage treatment becomes difficult and burdensome." Opponents warn that someone who is seriously ill could be pressured by friends or family to take her or his own life in order to avoid the high costs of medical care. In addition, notes a State Medical Association analysis of the measure, "We all know people who were told they had 'six months' to live and went on to live many months, even years, beyond that - often very happily." While the 7,000-member State Medical Association officially opposes the measure, a poll of members shows an even split between those for and against. The Roman Catholic Church has provided most of the funding for the campaign against 119. Also opposed are fundamentalist Protestant churches as well as anti-abortion groups which last spring launched "Operation White Rose" (named for the German medical students who resisted Adolf Hitler's euthanasia and genocide programs). Publicly supporting the measure are 175 doctors, 130 nurses, 100 social workers, and 240 members of the clergy. Proponents have been able to raise more money than those against the measure, much of it through the Oregon-based Hemlock Society. Recent surveys show a majority of those polled believe a doctor should not be prosecuted for helping a patient commit suicide.