THE INSTANT opposition to President Carter's proposal to control hospital costs was to be expected. The hospitals believe it will cripple their ability to provide medical services. Many doctors see it as a step toward controls on their fees. The labor unions think it is a device to limit wage increases. Some health planners regard it as a political tactic by which the administration can postpone pushing for the national health-insurance program the President promised during the campaign.

While there may be some truth in each of these objections, there is a far larger truth that these groups, as well as Congress and the rest of us have to face.It is that the primary objective right now in the health-care field must be to get skyrocketing costs under some semblance of control. And hospital charges are about 40 per cent of those costs.

The figures grow more staggering each year. In 1977, the nation's health-care bill will average $700 for each adult and child. The average stay in a hospital now produces a bill of $1,300, up 10 times over what it was in 1950. The total revenue of hospitals this year is expected to be around $64 billion. The federal government alone will spent $32 billion on Medicare and Medicaid in the next year, up 23 per cent, unless some immediate action is taken.

The problem with getting these costs under control is that there is no consensus among the experts about how to do it and very little incentive for those who determine the costs - the hospitals and doctors - to hold them down. Given the experience of the nation with Medicare, it seems clear that effective cost-control devices must be put in place either before a national health-insurance program is enacted or as a component of that program. The administration may have chosen wisely by going after the controls first.

That is not to suggest that the administration's proposal of a 9 per cent ceiling on increases in hospital bills is perfect. It amy be too arbitrary and inflexible, as the critics contend. But it seems to us that if it is, the burden of proof ought to be on the critics to make that case to Congress and to produce an acceptable alternative that will have the same result. Much has been said and written in the last few years about ways of holding costs down, but little has been done about such things as unneeded hospital beds, the acquisition of expensive equipment and the practice of defensive medicine that run cost up. Drastic steps are needed. If Congress doesn't like the administration's proposals for dealing with these urgent problems, it has a heavy obligation to respond constructively by coming up with practical and promising proposals of its own.