PRESIDENT REAGAN had some stirring words to say about freedom in his State of the Union address last Wednesday -- words that went well beyond his familiar commitment, which he repeated, to keep faith with those struggling in Afghanistan and Nicaragua "to defy Soviet-supported aggression." Declared the president: "Freedom is not the sole prerogative of a chosen few; it is the universal right of all God's children. . . . Our mission is to nourish and defend freedom and democracy and to communicate these ideals everywhere we can."

At this moment when the Reagan adminstration is rededicating itself to this goal, it is sobering to see the events that unfolded in South Korea in connection with the return of the opposition politician, Kim Dae Jung. Americans have expended much blood and treasure to build freedom and democracy in Korea over the last 30-plus years. Yet what has been on view in Seoul in recent days is a stark picture of a police-run society that uses force and deception to keep an opposition figure from taking up an orderly and peaceful role in the public life of his country. In addition, Americans accompanying Mr. Kim were, on evident official orders, physically abused -- an action for which their political tactics provided not the slightest justification. And the American Embassy itself, which thought it had worked out foolproof arrangements for a role of its own in the return proceedings, found itself helpless on the outside, duped by the very people in whom it had reposed its trust.

A brisk debate is under way over what were the elements of the arrival plan and who was responsible for its breakdown. The four major parties, Mr. Kim, his American escorts, the Korean government and the American government, have all contributed to it. It is important to learn just what happened, but it is also important to keep in central focus the question of why it is that freedom and democracy are in such apparent short supply in South Korea and what the United States ought to be doing in Korea, as the president put it, "to nourish and and defend freedom and democracy and to communicate these ideals everywhere we can."

If this is a legitimate goal of American policy -- and we believe it is -- then the implications for the United States in South Korea are very clear. Kim Dae Jung left Korea as a political exile in 1981. The Korean government greeted him by in effect restoring his condition as a political prisoner, immediately putting him back under house arrest. To fence off Mr. Kim and other opposition figures by "sedition" charges and police guards is a direct and -- one must assume -- deliberate affront to the policy freshly enunciated by Mr. Reagan. It is not the American escorts who are most challenged here: they are few and they are remote from the levers of official power. It is Ronald Reagan. What is he going to do about it?