WHO DID President Carter think he was - Harry Truman? And who did he think Maj. Gen. John K. Singlaub was - General of the Army Douglas MacArthur? That's what it looked like, briefly, and that is also, one had the impression, the way the White House wanted it to look. There was the angry, resolute President summarily recalling the insubordinate general from his Far Eastern duties to a face-to-face confrontation in the Oval Office and sternly dismissing him from his post. There also were the suitbly portentous, not-for-attribution elaborations from White House aides. The President, it was said, was determined to defend civilian supremacy over the armed forces against challenge by dissenting officers. And he was fearful, it was further explained, that the North Koreans might underestimate the American commitment to South Korea and undervalue the will and the capacity of the South Koreans to defend themselves - all on the strength of Gen. Singlaub's publicly stated estimation that if the United States proceeds with its plans for a phased withdrawal of its ground forces from South Korea, "it will lead to war."

Well, to take up the matter of North Korean miscalculation, we suppose it's possible, but only in the sense that anything is possible. For it is hard to believe that the North Koreans would make decisions on anything as important as an attack on South Korea on the basis of the indiscretions of one middlelevel American general. Our own view is that North Korean policymakers are quite capable of taking their own measure of South Korean capabilities. And their reading of American resolve in this matter is going to be largely influenced in the coming years by the firmness with which this country conveys its continuing commitment to South Korea, and by the deterrent effect of the U.S. air and naval forces that will still be on the scene.

There remains the principle at stake, having to do with civilian primacy in national-defense matters and with the need to enforce strict military discipline. And here, we would concede, Mr. Carter had a problem. His Korean-withdrawal plan was a firm campaign promise; its execution had been thoroughly debated in administration councils, and a high-level American delegation was about to leave for Seoul to work out the details with the South Koreans. Gen. Singlaub's timing could hardly have been worse. But his challenge to duly constituted authority and president Douglas MacArthur, who operated in systematic defiance of his commander-in-chief and raised in the sharpest terms, at home and aboard, the question of who was in charge. This was a case of a well-decorated combat officer of no intellectual pretensions, past his peak and destined only for retirement, making some irresponsible remarks. It required attention - by the Pentagon, we would have thought. High White House drama served only to give it far more significance and substance than it deserved.