The Vatican yesterday released a declaration that could make it easier for doctors, hospitals and patients themselves to decide to stop the use of costly life-support technology for terminally ill persons.

The 2,500-word statement, the Catholic Church's most comprehensive pronouncement on euthanasia in nearly 30 years, maintains the church's traditional ban on suicide, abortion and mercy killing. But new guidelines on using "extraordinary" means to pprolng life are expected to have a far-reaching impact.

The declaration said that doctors may "judge that, the investment in instruments are personnel is disproportionate to the results" that can be expected. It added that doctors may also decide that "the techniques applied impose on the patient strain or suffering out of proportion with the benefits" he may receive.

"When inevitable death is imminent in spite of the means used," the statement said, "it is permitted in conscience to take the decision to refuse forms of treatment that would only secure a precarious and burdensome prolongation of life, so long as the normal care due to the sick person in similar cases is not interrupted.

"In such circumstances the doctor has no reason to reproach himself with failing to help the person in danger," said the declaration, which was issued by the Vatican's Sacred Congregation for the Doctrine of the Faith. i

The patient also may ask that his life not be prolonged through extraordinary means, the document said. "Such a refusal is not the equivalent of suicide; on an acceptance of the human condition, or a wish to avoid the application of a medical procedure disproportionate to the results that can be expected or a desire not to impose excessive expense on the family or the community."

Because the Catholic Church has provided such a strong voice on questions of life and death in the past, the document is expected to have an impact beyond the church itself.

The Rev. Richard McCormick of the Kennedy Institute for Bioethics here, one of the leading Catholic theologians in the field, predicted that the new declaration "is going to support hospitals and physicians in doing what is clearly the right thing to do, in my view, in withdrawing respirators and other technology" from hopelessly ill or injured patients. At this time, he said, doctors often "have to go to court" to take such steps.

McCormick called the new statement a helpful document" that will counter "the overinvolvement of the courts in the management of the dying."

In recent years, there has been a proliferation of court battles over the right to turn off equipment used to sustain the vital functions of dying patients.

The most famous case involved Karen Ann Quinlan, a 21-year-old New Jersey woman whose Catholic parents had to get a court order before doctors would disconnect the life-support system that seemingly kept their comatose daughter alive. However, four years after the system was turned off, Quinlan continues to live, although she has not regained consciousness.

Bishop Thomas C. Kelley, general secretary for the American Catholic hierarchy, called the Vatican declaration "a timely and welcome statement."

Kelly said that "an unanticipated consequence of the progress of medical technology in recent years has been to add a new dimension of ethical complexity" to questions involving the sanctity of life. At the same time, he said, "there has been a disturbing deterioration of respect for life, not only before birth but after."

The statement said that doctors may, with the patient's consent, use experimental techniques or medications, even though they may entail "a certain risk. By accepting them, the patient can even show generosity in the service of humanity."

A section on painkillers and "the meaning of suffering for Christians" noted that "suffering, especially suffering during the last moments of life, has a special place in God's saving plan; it is in fact a sharing in Christ's passion and a union with the redeeming sacrifice which he offered . . ."

On narcotics, the document quotes Pope Pius VII, who held that narcotics could be used to deaden pain "if no other means exist" and if their use "does not prevent the carrying out of other religious and moral duties."

But painkillers that cause unconsciousness need "special consideration," the document said, "for a person not only has to be able to satisfy his or her moral duties and family obligations; he or she also has to prepare himself or herself with full consciousness for meeting Christ."

The document left no doubt that the church still opposes mercy killing, or the so-called right-to-die movement. "Nothing and no one can in any way permit the killing of an innocent human being, whether a fetus or an embryo, an infant or an adult, an old prson, or one suffering from an incurable disease, or a person who is dying," the statement said.

"Nothing and no one can in any way permit the killing of an innocent human being . . . No one is permitted to ask for the act of killing either for himself or herself or for another person . . . Nor can any authority legitimately recommend or permit such an action," the declaration said.

It was Pope Pius XII, who died in 1958, who did the most to develop Catholic thought on questions such as the use of "extraordinary" means to prolong life -- saying such measures were not required.

In the intervening years, however, medical technology has developed at such a fast pace that the "extraordinary" measures of Pius' day are now considered routine.

These advances, McCormick said make yesterday's statement an important one. It "walks the middle course between killing and overtreatment -- the two extremes we are confronted with today. It should be a helpful document."