The time-honored medical view that a human life is priceless and no cost should be spared to save it is no longer practical and must be replaced in part by modern cost-benefit analysis, four Harvard medical professors said yesterday.

"A new era" has started in which "we are developing life-saving methods well beyond our capacity to pay for them," and "national priorities" must be set to decide who should be helped and by what methods, the professors said.

Dr. Howard Hiatt, dean of the Harvard School of Public Health, endorsed the cost-benefit approach as presented in a new study by three co-workers, Drs. Benjamin Barnes, John Bunker and Frederick Mosteller. The four appeared at a news conference at the National Press Club.

Hiatt said the news conference was held in Washington to call the attention of the American public and law-makers to the need to find new methods of medical decision-making.

What makes this urgent, he added, is the nation's fast-growing health bill - $139 billion in 1976, perhaps $160 billion this year - aggravated by expensive tools such as kidney dialysis, coronary heart surgery and artificial means of keeping people alive.

Also adding to the health bill is the fact that surgery of all kinds has increased 14 per cent since 1970, said Barnes, to the point where 18 million operations were done last year.

Among "questionable" procedures in may cases the Harvard group listed hysterectomies and tonsillectomies, done by the thousands, and radical breast operations in cases where a lesser operation with other treatment may have just as good results.

The questionable operations, they said, include appendectomies on "marginal" patients - those with minimal symptoms and little chance of more serious disease or death of not operated on.

So many appendectomies are being done for symptoms that cause few deaths that "we are now putting tens of thousands of people in the hospital each year at a cost of $43 million to save each additional life," Mosteller said.

What he meant, he said, was that many appendectomies are bing performed each year, at great cost, on people with minor symptoms, and that if they were nover operated on, the death rate would be only one in many thousands.

"We're talking about many operations with only marginal effects," Hiatt said.

"We need much new data-gathering on such operations" outcomes. We need to know about comfort and relief of disabilities as well as lives.

"When we have more data, we can make better decisions, including what procedures the public should be willing to pay for."

The decision-making method the Harvard group suggested is addition of economic techniques such as cost-benefit analysis and statistical studies to the traditional doctor-patient relationship.

For example, a doctor considering an operating might weigh a patient's symptoms against national statistics showing what happens if such patients are or are not operated on; what risks occur if the operation is or is not done, and what the cost to the patient and society might be in terms of dollars, discomfort and life-saving.

"The physician treating the individual patient still has to make the final decision about how to treat an illness and we should not lose sight of that," Mosteller said. "But he could be given a good deal of help by modern methods."

Mosteller is a noted statistician and head of biostatistics in the Harvard School of Public Health. Barnes is a Harvard surgeon and bunker is a Stanford University anesthesia professor who has been a visiting professor at Harvard. Their study has been published as a book titled "Costs, Risks and Benefits of Surgery."

With Hiatt, the group recommended training medical students and doctors in cost-benefit analysis and involving patients and the public in the decisions.

According to one study of 850,000 operations in 34 hospitals, there are nearly two deaths in every 1,000 operations - and one death in 10 is caused by the anesthetic. If people are given facts such as these, they will help their doctors decide when not to operate, the Harvard group said.