WHAT IS HAPPENING now in Poland is fantastic. Pope John Paul II, conducting a "religious pilgrimage" to his native land, is demonstrating a command of the loyalties of the people which in a democratic country would entitle him to be their secular as well as their religious leader. The Communist authorities are being revealed, in a manner even more telling than in the open revolts against their rule in 1956 and 1970, as bereft of similar popular support - i.e., legitimacy. The authorities have never before allowed a pope to enter what remains after 30 years of Communist power, a profoundly Catholic nation. They have been forced not only to invite John Paul II but to receive him with honors and to try as best they can do to ride out the currents generated by his trip.

Poland, of course, has a special history. As the pope's program yesterday demonstrated, the Catholic Church has been identified with Polish nationalism far more than its secular rulers have, especially the current rulers. They had two strikes against them to start; they were imposed by a traditionally hated foreign power, the Soviet Union, and they profess atheism. A potential third strike lies in their inability to master Poland's formidable economic strains.

This is what imparts the special edge of drama to the pope's visit. Despite his effortto stay within the bounds - to him the broad bounds - of the religious sphere, the emotions he has let loose are evident in the size and fervor of the crowds he is drawing, and there could yet be an explosion. The fragility of the Communist order in Poland, elsewhere in Eastern Europe and even, to an extent harder to express (and therefore to measure), in the Soviet Union itself, is a political fact. What John Paul II, self-styled "Slav pope,) yesterday called "the spiritual unity of Christian Europe" is also a political fact. This puts a heavy responsibility on John Paul II and, in this instance, on Communist party leader Edward Gierek, a figure sensitive in his own way to both the constraints on Poland and the aspirations of Poles.

Yet the pope's "pilgrimage" indicates more than the historical and political forces at play. An extraordinary personality, authentic and resonant, has been unfolding since Karol Jozef Wojtyla became Pope John Paul II last October. His trip has already shown he has a politican's touch with the common people.A rare sense of public theater has been harnessed to his determination to try to make the church live and vibrant to the faithful, especially the young. On some matters of vital social concern to Catholics and non-Catholics alike around the world, he has taken unfortunate positions. But his intellectuality does give him an added way to make his faith relevant and competitive in a world of diverse distractions and ideologies. And having lived under fascism as well as communism, he has unmatched personal credentials for evaluating secular power.

In sum, John Paul II projects a sense of being uniquely qualified to strike a new religious-secular balance. This accounts for the near-universal fascination with theman, and for the absorption in what his audiences yesterday described as his trip "home."