NORTH KOREA, by shooting down a strayed and unarmed American helicopter, has reminded the world that its masters are brutal people. More to the point, it has embarrassed Jimmy Carter. For, while many Americans will conclude that the latest incident at the DMZ demonstrates how dangerous Korea remains and how desirable it would be for the United States to step back, many others will read it quite another way. If Korea remains so dangerous, they will ask, why is the President pulling out American ground forces before any start has been made on resolving the political differences that create the danger? The question takes on added sharpness from the coincidental disclosure that the President overrode a recommendation by the Joint Chiefs of Staff that only 7,000 troops be withdrawn over the next five years. They accepted Mr. Carter's decision to pull out all 33,000 over the same period only on condition that Seoul get large amounts of extra aid to help make up the difference.

With this in mind, it becomes easier to understand President Carter's conspicuously low-key response to the incident. He let it be known that he had been attentive to the crisis but had lost no sleep because of it. His press secretary was quick to characterize the helicopter's incursion into North Korea as unintentional and regrettable and as an isolated incident apparently unrelated to any larger North Korean plan of aggression. U.S. military spokesmen emphasized that the rough response was entirely consistent with North Korea's past policy and, presumably, not to be read as some calculated new provocation. Rejecting the option (used in the last incident by President Ford) of calling a military alert, Mr. Carter chose instead to follow a conciliatory procedure looking to an early meeting, with the North Koreans.

Obviously, Mr. Carter has a responsibility to rescue the helicopter's sole survivor, now a prisoner, and to reclaim the bodies of the three airmen lost. Perhaps, too, he had it in mind, in his first military minicrisis, to create a certain appearance of coolness and sureness. But most of all he seemed to be trying to preserve the sort of business-as-usual atmosphere that would help win support for his troop-withdrawal decision.

We think he's right to treat the incident that way. The rationale for troop withdrawal is not that the North Koreans have somehow become more congenial. It is that the security of South Korea can now be upheld by means other than the continued stationing of American forces on the ground. The superpatriots find it easy to demand that American honor be avenged. But it is not American honor that has been challenged; it is American good sense that is, as always, being tested.

When the prisoner and the bodies of the three casualties have been returned, Mr. Carter should explain why the incident ought not to be allowed to alter his withdrawal plans. At the same time, and for the same purpose of enhancing confidence, he should explain why he chose to ignore the advice of the Joint Chiefs to pull out just 7,000 men over the next five years. We think there is a satisfactory answer. Diplomacy and politics alike demand that he offer it.