A HEADLINE that caught our eye the other day said, "FDA Sees $2-Billion Saving by Halting Unneeded X-Rays." The story quoted the chief of the Food and Drug Administration as having estimated that 30 per cent of all diagnostic X-rays are unnecessary. It seems they are ordered by doctors who are practicing defensive medicine, not just diagnostic medicine.Evidently these X-rays - some 60 million a year - are a kind of insurance the doctors take out against subsequent questioning of their judgment, if their diagnosis should turn out to have been wrong.

This is the most recent of several reports suggesting that excess of one kind or another are responsible for part of the nation's staggering medical bill. And it, most likely, will be caught in the same argument that has developed around the others. Take, for example, proposals that the building of hospitals and the installation of high-cost equipment be regulated so that a community does not find itself with an excess of either. The reason for such limits is that neither patients nor insurance companies should have to bear the costs of beds or equipment a community doesn't need. The argument against such restrictions, made forcefully by some doctors, is that they interfere with practice of medicine. That argument would apply even more forcefully to any regulation or, even, guideline on the ordering of X-rays.

Yet, drastic steps need to be taken to get the costs of medical care under control. Anyone who has paid a medical bill or and insurance premium knows that the recent rate of increase in those costs cannot be permitted to continue. So we welcome the finding of FDA Commissioner Donald Kennedy that the use of X-ray equipment is an area where significant cuts can be made. But getting them made is something else again. And, it is here, or so it seems to us, that the self interests of the medical profession and the pocket-book interests of the rest of use begin to coincide.

The development of what is called defensive medicine is, to a large extent, the result of the increase in medical malpractice suits. And the $2-billion tag on unneeded X-rays is only part of the cost of this kind of medicine; millions of other kinds of tests are ordered annually by doctors who want them on file as evidence they haven't neglected anything. Thus, any program that FDA or anyone else dreams up to try to get the X-ray situation under control is unlikely to make a substantial dent in overall medical costs until the malpratice situation is brought under control.

We wish that we or anyone else knew of a clear and demonstrably correct solution to this aspect (or any of the others) of the medical-cost crisis. A citizens' commission in California recently called for a sweeping overhaul of the tort system, not just as it affects medical malpractice cases but as it affects all personal-injury and liability lawsuits. That may well be one of the roads that need to be followed. But while doctors, lawyers, citizens' commissions and legislatures struggle with the high costs of getting well and staying well, the rest of us will continue to pay - excessively. FDA's hopes of cutting back on unneeded X-rays are worth pursuing - every little bit helps. But any success needs to be seen in the perspective of a problem that may have to get worse before the country is ready for the drastic surgery need to make it better.