MUCH OF THE consideration of the new administration's policy toward South Korea comes down to a measure of the choice President Reagan has supposedly made between security goals and human rights goals. Either Reagan is saluted for coming down hard on the security side, which he unquestionably did during the visit of the new South Korean president this week, or he is scolded for stinting publicly on the human rights side, which he also unquestionably did while Chun Doo Hwan was here. The common assumption seems to be that it is a zero-sum game: to gain on one side, you must figure to lose on the other.

But is this so? The striking feature of South Korea in the last four years is instability, including the assassination of strongman Park Chung Hee and the subsequent seizure of power by a protege, Mr. Chun. In the process, the condition of human rights sharply deteriorated. This was a disappointment to Mr. Carter. But for what should he be judged -- for his enthusiasm for the cause or for the actual results? A case can be made that some part of the deterioration arose from the uncertainties he inadvertently fed, first, by his unstudied unilateral decision to reduce American forces and, second, by treating human rights in a way that some powerful Koreans saw as a threat to their power. As painful as the exercise may be, those who most prize human rights have special reason to ponder the record. b

Does this mean that the flip side is true and that a security-first policy in Washington will produce a liberal blooming in Seoul? Don't bet on it. And don't confuse the commutation of gadfy Kim Dae Jung's death sentence, welcome as it is, with "human rights": he was spared as part of a deal that gave the new American administration the security posture it wanted in East Asia and the new Korean regime the political boon of a return to American favor. Mr. Chun is still running South Korea as a police state.

At the same time, the handful of Koreans who run their country deserve a chance to show what they can do when they are not faced with either what they perceive as an erosion of their American security guarantee or direct American pressure on the human rights front. Koreans have the political skill, the economic base and a possible reason -- national pride -- to make their system more democratic if they choose. We are not optimistic. But it would be hard for things to get worse than they were in the last four years.