TRUE, THE CARTER administration's first sketch for a national health insurance plan has gingerly and tentative air to it. But if there is any public responsibility in which caution is a virtue, it is this one. The way in which the country pays for it strongly influences the kind of medical care that people get. Would you rather take your aches to a family doctor or to a clinic? Should the payments system be tilted toward caring for people in hospitals, as it now is, or toward caring for them at home? How much of the money ought to go into helping the sick, and how much for preventive medicine?

But over the last few days, the quarrel has been entirely among the people who strongly support national health insurance, and it has been entirely over political tactics. The leading congressional advocate of comprehensive insurance, Sen. Edward M. Kennedy (D-Mass.), is at odds with the administration on the way to build the tremendous momentum, throughout the rest of the country as well as here in Washington, that is necessary to pass legislation of this magnitude.

When the administration announced on Saturday its list of health-policy principles - not a bill, but the outline of a future bill - it emphasized that each stage of its plan would be contingent on economic conditions. Sen. Kennedy argues that people will not support a bill that makes only conditional promises. A bill will capture the voters' enthusiasm, he believes, only if it phases in the new protection on a set schedule on which the public can count. Secretary of Health, Education and Welfare Joseph A. Californo objects that in some future recession the federal government might want to spend its money temporarily on creating jobs, for example, rather than on the next step in expanding health insurance. But that is exactly the kind of choice - jobs versus health care - that the senator does not want to leave to future Congresses.

If at some future time the increase in insurance should merely appear to inflate costs without adding much to the quality of care, Mr. Califano would want the authority to halt further increases until the cost controls are sharpened. Sen. Kennedy takes the opposite view. Only the explicit promise of a guaranteed program, he objects, will generate a constituency broad and powerful enough to push effective cost controls through Congress.

Controlling costs is the heart of the matter. The campaign for comprehensive health insurance bears the burden of the experience under Medicare and Medicaid. When they were enacted, they were accompanied by only the most vague and modest financial estimates. But the rapid inflation in hospital bills dates back to 1966, the year that those two programs went into effect. By 1968, the two programs together cost $7 billion. By 1974, they were up to $17 billion. This year, they have more than doubled again to $37 billion. They provide indispensable protection to the elderly and the poor. Nobody wants to take that protection away. But those soaring figures constitute a warning. The administration has been trying since last winter to get through Congress a bill to contain the rapid rise in hospital costs. Two weeks ago, in the House, that effort collapsed - an evil omen for any larger bill ahead.

National health insurance is highly desirable - eventually, if not immediately. But the tide in politics throughout the country is running strongly in favor of less federal spending, lower taxes and less government intervention. The budget is tighter, and inflation more intractable, than anyone expected when Mr. Carter first promised health insurance. It's difficult to believe that, under the present circumstances, Congress would enact anything worth having. When Mr. Califano brought out the administration's principles, he was, in effect, asking for a showing of broad public support. Sen. Kennedy will be doing the same thing when, later this year, he holds hearings on his own bill. So far, you would have to say, the response has not been encouraging.