THE RECLUSIVE leaders of Stalinist North Korea are often described as irrational and unpredictable, but that's not quite right. For locking their 21 million people into what is essentially one country-sized concentration camp, and for condemning many of them to die by starvation, North Korea's leaders can fairly be described as evil. By isolating themselves behind their failed ideology of self-reliance, they also increase the likelihood of misunderstanding between them and the rest of the world. But in promoting its own survival, and manipulating other nations on its own behalf, North Korea's regime is far from irrational.

That became clear again with the latest achievement in U.S.-North Korean diplomacy. North Korea had threatened to test-fly a new, long-range missile capable of delivering weapons to parts of the United States. Such a launch would have heightened tensions throughout Northeast Asia. The United States and its allies, Japan and South Korea, threatened adverse consequences if North Korea tested the missiles and proffered benefits if North Korea desisted. So North Korea, at least for now, apparently has decided not to test.

There is something distasteful in this transaction, which fits neatly into a pattern of North Korean behavior that, anywhere outside diplomatic circles, would be known as blackmail. North Korea's Communist leaders threaten to do something inimical to world peace (build a nuclear weapon, sell arms to war zones, launch missiles over Japan). If it then restrains itself, it is rewarded for not doing what it shouldn't have done in the first place. In theory, North Korea could play this game indefinitely, at no cost to itself.

But this latest outcome gives at least some hope for a break in the pattern. In following a policy now being fashioned, at President Clinton's request, by former defense secretary William Perry, the United States and its allies seemed as serious about sanctions as about rewards. The three nations -- the United States, Japan and South Korea -- remained united, also something that hasn't always held true in the past. As far as is publicly known, the allies didn't promise anything unseemly in the way of inducements.

So it is reasonable now for national security adviser Sandy Berger to speak, as he did yesterday, about "some easing of economic sanctions." This is not direct assistance; in fact, given the bankruptcy of North Korea's economy and its economic policy, such an easing isn't likely to have much practical effect. But it has the advantage of supporting the "Sunshine Policy" of South Korean President Kim Dae Jung, an elected leader who merits considerable deference in this matter. And it might persuade North Korea's regime to begin looking for ways other than blackmail to interact with the rest of the world.