LAST YEAR Americans spent over $200 billion on health care. That's about 9 percent of GNP. In return they got what is probably the best overall health care in the world. The many that seems a reasonable deal. But every now and then something startling comes to light about the way health care is made available to people. s

Take the case of John Reed, reported in this paper the other day. Mr. Reed's fourth child was born with severe congenital defects. Keeping the child alive has cost over $100,000. Laid off from his job, the father has no health insurance and has rejected several $200,000-a-year job offers because the companies are unwilling to cover the child under their health plans. So taxpayers end up paying for both the medical costs (through Medicaid, medical assistance for poor families) and the general support of the family (through unemployment benefits).

One seemingly obvious remedy would be national catastrophic health insurance, protection against ruinous health care expenses. Former Sen. Schweiker, Mr. Reagan's choice for secretary of HHS, has expressed support for requiring this kind of coverage, at least for employed workers, and the idea enjoys widespread support. The trouble is that America's medical care system is already geared too much toward providing very expensive, high-technology care to a relatively small number of people -- and to do this at the expense of preventive or early treatment care for millions of others. Providing guaranteed reimbursment only for high-cost care may channel more resources into the expensive and esoteric kinds of treatment that have relatively little effect on general health or longevity.

Preventing such skewing of the health care system isn't easy. The problem is not in covering acute illnesses like strokes, heart attacks and treatable cancers. Although these can quickly bankrupt a family or even a small firm, the total national cost is not large. The problem lies in deciding how much treatment makes sense, and for how long, for those patients for whom medical care offers no possibility of recovery. Responsible physicians and hospitals make these decisions daily, but on a personal basis with detailed knowledge of the patient's comfort and possibilities. Legislating general standards and public reviews may make physicians less willing and able to shoulder this difficult burden.

There is no easy way to fill in the gaps in national health care coverage. Private companies won't do it for sound financial reasons. If the government does it, it is a delusion to think that costs can be limited to coverning a few heartache cases. The whole structure and cost of the medical system will be affected. To prevent that, it is necessary to balance catastrophic coverage with extensions of preventive care and with built-in controls.