Doctors are increasingly asking the troubling question: can society afford all the expensive new things we know how to do?

Doctors from four medical centers ask it about two areas of medicine -- heart transplants and cancer treatment -- in the current New England Journal of Medicine.

On whether to start a heart transplant program at Massachusetts General Hospital in Boston, the hospital's chief of medical service, Dr. Alexander Leaf, answers an emphatic no.

He agrees with the hospital's trustees, who decided three months ago not to allow heart transplants, because they would cost more than $100,000 each on the average, and drain resources from other patients, who might be helped more by that much money.

Only Stanford Medical Center now does heart transplants with any regularity or great success. Half of its recent patients have survived for five years, at costs ranging from $35,000 to $200,000 each.

Doctors gave a more complicated answer to another question: Should doctors give more bone marrow transplants, at $1,700 each, to try to save more acute leukemia patients?

Dr. Emil Freireich of M.D. Anderson Cancer Hospital in Houston answers an almost passionate yes in a New England Journal editorial. He says such methods, although "still primitive," can offer life to many future patients, if properly developed.

Dr. Karl Blume and associates at City of Hope Medical Center near Los Angeles recommend some bone marrow transplants, but do so cautiously and bring up their great cost.

Dr. Marc Rosenshein and colleagues of the Puget Sound Blood Center and University of Washington performed a "cost-effectiveness" study of white blood cell or leukocyte transfusions for leukemics. Making them more routine could add $75 million to the nation's growing medical bill, they conclude.

The cost to society of each year of life saved would be from $35,000 to $85,000, they calculate. They call these figures "extremely marginal," a cost-analyst's way of saying the public might want to spend the money otherwise.

These discussions are part of a growing attempt by the New England Journal to ask about the dollar cost of new medical methods. The journal recently reported that many heart patients could move, from costly intensive-care units earlier, without harm.

"We are now investing such vast resources in intensive care," said Dr. Arnold Relman, the journal's editor, "that we must begin to take stock of what we are doing."

The journal's reports on bone marrow and white blood cell transplants for acute leukemia patients confirm others which say these techniques may lengthen some lives.

Doctors have had striking success with combinations of chemicals in treating childhood leukemia. Fifty to 75 percent of such children now live five years or more, and many are apparently cured.

But the latest nationally calculated five-year survival rate for adults with acute leukemia is still only 5 percent.

At least half of adults on chemotherapy for leukemia might benefit from white blood cell transfusions, said Freireich, who developed the technique.

About 10 percent, he said, might benefit from whole-body radiation to kill their diseased bone marrow, followed by a transfusion of new bone marrow from a donor. The best candidates for this treatment, he said, are "those who respond best to chemotherapy and are in remission," yet "still at high risk" of further disease.

There is still trouble finding a compatible marrow donor for more than a fourth or fifth of these patients, he said. And though every major medical center is now doing such transplants, he reported, the actual number of transplants is still very small because of the cost.

In this and many ways, he said, a squeeze in funds, federal and otherwise, is already forcing hospitals to limit some kinds of care. He called this very bad.

But Massachusetts General Hospital, sometimes called "the nation's best," six years ago established a Resource Allocation Board to rule on doubtful new requests for added staff or machines or costly tests or procedures. It has so far reviewed 28 requests, approved 15 and turned down 13, and has been overruled only once by the hosptial's director.