What are the causes of our zooming national medical bill? We have heard much of inflated insurance, inflated hospital and doctors' bills, expensive new technology, inefficiency, and a growing population over 65. To temper these forces, both political parties have set forth plans to increase competition in the medical system, to place medical care on a budget, or to do both, as the current administration wants to do.

But how about the most wasteful item on our medical-care bill, an item no plan addresses: bad medical care?

Bad medical care initiated or allowed by doctors costs Americans in excess of $10 billion a year in reparative treatment and patients' forfeited wages, according to Elliott Segal, former director of the health task force of the congressional subcommittee on oversight and investigation, which investigated unnecessary and incompetent surgery.

This the medical profession knows very well. A recent article in The New England Journal of Medicine begins: "Among the controlling factors that contribute to the high cost of medical care, complications arising from physicians' errors looms large." The authors, all on the faculty of the Harvard Medical School, go on to report that in one year, a well-known Boston medical center admitted 36 patients suffering from mishaps that occurred during surgery; in 24 cases, errors had been committed by physicians.

In an article describing a different set of surgical slip-ups, the same authors tell us that they are "impressed by the unremitting abundance of . . . misadventures" that occur during commonplace operations and the consequent need for costly remedial care afterward.

Similarly, a review called "Surgery in the United States, A Summary Report of Surgical Services for the United States," published in 1975, found that 78 percent of the preventable deaths and complications occurring during routine operations over the five years studied could be attributed to surgeons. Faulty surgical technique was blamed in 65 percent of the cases, with poor judgment or flawed diagnosis implied in 11 percent.

Altogether contrary to the public's belief, a good portion of this bad care occurs just where it's not supposed to: in teaching hospitals. Nor is it confined to the operating rooms. In another recent article in The New England Journal of Medicine, Dr. Knight Steel of Boston University Medical Center asserts that 36 percent of 815 consecutive patients of the general medical service of that hospital suffered from diseases caused by diagnostic or therapeutic treatment errors made on the premises.

If the medical profession were seriously trying to discover the source of all this failure, the system of medical education would seem a reasonable subject for its investigation. Central to that education is the well-documented fact that the treatment of patients, both clinic and private, in teaching hospitals is largely in the hands of residents, many not a year out of medical school. Is this fact quite unconnected to the large error rate in hospitals whose staffs of specialists are among the most renowned in their fields?

The profession routinely insists that patient care is just as good when given by a resident under supervision of a private physician as it is when given by the private physician himself. Yet the fact is that there is no serious evidence to back up this claim--only doctors' private observations. In the same realm of experience and mere opinion, however, quite a few books on other aspects of medical practice have in passing had disturbing things to say about resident care of patients.

Charles Bosk writes in "Forgive and Remember": "The insertion of a subclavian catheter can be a very tricky business. It requires poise and confidence. It should be carefully supervised. Unfortunately, it is one of those procedures that we are least likely to monitor. All too often, we instruct our residents to insert subclavian catheters as we walk off the floor on our way home for the night. . . . We cannot always count on our house staff to properly assess the trickiness of techniques.

And in "The Making of a Surgeon," Dr. William Nolan describes his first major surgical procedure during residency, a routine appendectomy under the supervision of a seasoned physician. Young Nolan began the operation by pressing down too hard with his scalpel, cutting too deeply. He forgot how to tie knots to seal off blood vessels and at one point tied the end of his rubber glove into the wound. He had trouble finding the appendix. When he did find it, he cut it off clumsily, undoing the knot in it. Finally, he let the appendix pop back into the abdomen, causing an infection. The patient, not surprisingly, had a long and complicated convalescence. One doubts that if Nolan performed the same operation today, he and his patient would have the same troubles.

Is it possible that at least some of the length and expensive convalescences described in The New England Journal of Medicine article were caused by the sort of resident inexperience described by Bosk and Nolan? One would think that the profession would want to know. Dr. George Melcher, the former head of Group Health Insurance, says that a study was done at Mt. Sinai Hospital in Miami and that it showed a statistically significant difference in the mortality and morbidity rates among patients operated on by surgeons and those operated on by supervised residents. But he said it was never published, and Mt. Sinai told me it has no such study in its files.

It has been suggested that such a study would be futile, because even if it found that residents jeopardize patients' care, what would be the alternative? Doctors in training need to practice medicine on living patients--to learn how to practice medicine. To this, one can only reply that until and unless a problem is established, no serious thought will be given to its solution.

Moreover, a study of residency education might answer other questions. Many residents are dissatisfied with their current wage. Are they students or doctors, and, according to the answer to that legitimate question, what are their services worth? Then, too, a study might determine whether the residents who make the most mistakes today go on to be the doctors who make the most mistakes tomorrow, and whether those residents need more (or a different kind of) training. It might also, by comparing patient casualties among residency programs, determine which programs provide the best education while best protecting patients.

In medicine, as in much else, ignorance is not bliss. It generates misery and death and costs billions of dollars.