VATICAN CITY, SEPT. 9 -- Pope John Paul II arrives in Miami Thursday as history's most visible pope. In 35 trips outside Italy since 1978, he has been seen by more people in more places than all of his predecessors since the fisherman Peter became the first pope in 64 A.D.

This 10-day U.S. tour makes No. 36.

Yet the engaging, blue-eyed 67-year-old pontiff from Poland remains enigmatic -- described simultaneously as a stern, old-fashioned, even curmudgeonly disciplinarian in defense of church teachings on morality and a thoroughly modern, cosmopolitan activist for social, economic and political justice.

The apparent contradictions are bound together by his charisma: His way with people -- one by one or in enormous crowds -- has made him a media "superstar" and draws even those who do not share his views.

"Whatever anyone says about this pope, this is a man who knows how to lead, to influence people, to move people," said an American priest here who has watched him from the beginning of his papacy. "He is robust, articulate, athletic, energetic and self-assured, and because of this, his very physical presence, even more than his message, has given new life to the papacy."

Unlike his mostly sedentary predecessors, he craves activity. He is a sportsman who still skis, hikes, canoes and swims.

Though he can be gregarious and outgoing, he is also contemplative and, on matters of principle, stubborn. Close associates say his expansive warmth can cool rapidly when his beliefs meet with resistence, and at times, his temper is said to be fierce.

"He is very difficult to define," said the Rev. John Navone, a Jesuit theology professor at the Vatican's Gregorian University in Rome. "The usual conservative and liberal categories we all want to use simply don't fit with him, because he embraces both."

Under this pope, the Vatican's crackdowns on theologians, priests or nuns who have challenged church doctrine in such controversial areas as papal authority or its teachings on divorce, birth control, abortion and the limited role of women in the church are well known.

So are his confrontations with such dictators as Gen. Wojciech Jaruzelski in his native Poland or Gen. Augusto Pinochet of Chile, whom he has lectured on the imperatives of human rights and the ills of repression.

"Pope John Paul II . . . cannot be understood merely in terms of his separate actions or views on this or that issue," said a senior Vatican prelate who has worked closely with him and asked, like most church officials here, not to be named. "The man is more than a sum of his parts. Despite the common view, there is no duality in his vision."

But it is a complex vision, fashioned from relatively simple origins and a diverse career. Born Karol Wojtyla, he has been a factory worker, a stonemason, a student leader, playwright, philosopher, parish priest, cardinal and archbishop of Cracow. (Like President Reagan, who will greet him in Miami, he is also a former actor.)

He lived through the horror of Poland's occupation by Adolf Hitler in World War II, then with the equally unpalatable results of Stalin's "liberation," which gave him a lasting distaste for marxism. But that does not make him an admirer of western capitalism, whose affluence he suspects.

Many Vatican officials initially feared that Poland, and the Polish church, would preoccupy the new pope, but he dispelled their fears. "He was born in Poland, but his mind is of a much wider horizon," said a high-ranking Vatican cleric. "He has transcended his Polishness."

Even before he became pope, Wojtyla traveled as widely as his ecclesiastical duties and the communist government allowed. As a cardinal, he made at least 24 extensive trips abroad -- to the United States, Latin America, even as far afield as Papua New Guinea.

He has mastered seven languages and learned the rudiments of a dozen others. He is conversant with modern science. He said to have a thorough grasp of political and social problems in most regions and nations. He has an open, curious mind, as befits a priest who was a professor of ethics at Poland's Catholic University at Lublin.

Vatican spokesman Joaquin Navarro said the pontiff's "clear vision of the church that governs all of his actions and pronouncements" includes a duty "to stress the ethical dimension of all human problems:" poverty, racial discrimination, arms control. He rarely misses a chance to speak on such topics.

But the pope believes the church also "must be strong and true to itself," Navarro said. He is at his most inflexible on church doctrine and teachings, deeply marked by the Roman Catholic Church's 1,000 years of rigid unity in defiance of temporal attempts to destroy Poland. The Polish church embodied Polish nationalism, and maintaining a strong, united, disciplined church meant unquestioned adherence to its precepts.

Pope John Paul II was selected Oct. 16, 1978, precisely because most of the church's College of Cardinals believed that 20 years of Vatican Council reforms, which redefined the church as the whole people of God and sought to make worship more accessible to the laity, had begun to erode the church's foundations.

"The pope came in with a mandate to unite a church increasingly divided over the various -- liberal and conservative -- reinterpretations of the Vatican Council," a senior Vatican prelate said. "There were doubts among the faithful about just what the church really was, and it has been up to him to dispel them."