There is a kind of mind-blowing artlessness to Ronald Reagan's comments on communism. He speaks with equanimity and certainty of things that others regard with astonishment and doubt. Such as the breakup of the Soviet empire and the disintegration of communist rule at home. Sharpening a now-familiar theme, he said this week that communism is an "aberration . . . not a normal way of living for human beings." We are seeing "the beginning of the end."

Never mind that, as he uttered this blanket indictment of "communism," his secretary of state was wrapping up new arms package in Peking. Let us take his principal target as Soviet communism. Prophecies like his have been heard since the Red Army overran Eastern Europe in World War II, and before. Until now, however, it has usually been thought illusory or impractical to believe that communist rule, besides being cruel, wouldn't last. People who so believed were labeled cold warriors. The theory of detente has always been that communism is here to stay: therefore, learn to live with it.

What gives the contrary outlook currency is the Reagan-Poland connection. Events there are transforming his views on communism from dubious history and personal idiosyncrasy into empirical observations on a reality unfolding before our eyes. However anachronistic or wishful Reagan's views may appear, it is hard to fault him for sying that communism is an aberration and the empire is crackling, when the Polish people are vindicating that judgment day by day.

The Poles are making Reagan look good not only as a political analyst but also as a moralist. For years he has been ready and waiting for them to catch up to his expectations of their freedom. He has always seen Yalta as a mighty breach of faith. At that wartime conference, the United States cut a deal for postwar influence, in effect consigning East Europe to Moscow's sphere.

Now Reagan sees the Soviet Union "faced with the problem of this crack in their once-Iron Curtain, and what happens if they let it go. But on the other hand, what is going to be the impact if they take a forceful action . . ." He summarizes precisely the dilemma the Soviets have created for themselves. And while he has taken a few actions that tend to help them get out of it -- selling grain to Moscow, for instance, and providing modest food and debt relief to Warsaw -- plainly his larger intent is to watch them squirm.

Earlier administrations put a premium on stability in Europe. They feared, with "realists" and advocates of detente in warm greement, that too-precipitate a change in the East tempted Soviet reprisal and might spill over into the West, producing even World War III. Reagan puts a premium on instability -- in East Europe. He does not blink at the prospect of reprisal and shows a cool indifference to any prospect of spillover.

It is not for Reagan, moreover, to make the argument that I have hoped would be getting a serious hearing in the Politburo. Namely, that Poland with its own culture and history is a special case, that what happens in that country will not necessarily spread to other lands of the Soviet realm, that a "renewed" Poland will stay within the traces of Communist Party rule and the Soviet alliance system, and that therefore Moscow had best grit its teeth and make do.

On the contrary, Reagan undercuts the special-case argument by setting what is happening in Poland against a general crisis of communism. He took this giant leap on Tuesday: "the things we're seeing not only in Poland but the reports that are beginning to come out of Russia itself about the younger generation and its resistance to longtime government controls [are] an indication that communism is an aberration . . . the beginning of the end." He evidently had particular reference to a recent lament about Soviet youth by the head of the KGB. But there he was applying the Polish spark to Soviet tinder and blowing on the flame.

Reagan has made a choice: to keep faith with the Poles, to support what he regards as their liberation struggle by all means diplomatically and politically feasible including ties with China, to cast not even a shadow of a suggestion that the Poles should alter their course for the sake of other countries. No matter what happens in Poland, he appears to believe, the idea if not the fact of freedom will be strengthened and the strategic position of the Soviet Union weakened.

I am not without respect for the president's approach to the Polish question. But I wonder whether the Soviet leaders may find Reagan so sweepingly committed to doing them in, regardless of what they do in Poland, that they shed what incentive they still may have to do the right thing.