Before considering John Paul II, the pope who brings something truly new to the American experience when he begins traveling the United States after his arrival in Boston Monday, let us recall John Adams. That crusty apostle of liberty and freedom, as much an architect of the American democratic system as anyone, had attended a Roman Catholic service in Philadelphia at the time of the Revolution. He found it, as he wrote his wife Abigail:

"Most awful and affecting: the poor wretches fingering their beads, chanting Latin, not a word of which they understood; their paternosters and ave marias; their holy water; their crossing themselves perpetually; their bowing and kneeling and genuflecting before the altar."

For almost two centuries many in America's non-Catholic majority shared Adams' unease about the followers of a faith led by an infallible pope sitting on a throne in far-off Rome. A conflict of many parts -- between church and state, dogma and dissent, authoritarianism and democracy, old world and new -- has long weighed against an official American visit by a reigning pope.

It is little wonder, then, that the pope's week-long American tour has stirred such interest and evoked such deep historical memories.

Not that John Paul II, the 264th successor of St. Peter in the See of Rome, will be the first pontiff to set foot on American soil. Paul VI, who broke the ages-old pattern that made popes "prisoners of the Vatican" when he began traveling outside of Italy, spent 13 hectic hours in the United States almost exactly 14 years ago to the day John Paul arrives. But his trip was made at the specific invitation of the United Nations and was confined to New York City.

President Lyndon Johnson, instead of inviting the pope to the White House as Jimmy Carter has done with John Paul, had a 45-minute private discussion with him in the Waldorf-Astoria Hotel after the pontiff addressed the U.N.'s General Assembly.

There is therefore no precedent for this pope's trip.

Where he goes and what he says will make not only news, but also history. Beyond this, there is the character and personality of the man who delivers the first papal message personally to Americans, visits six of their cities, meets with their president in the White House, and celebrates an open-air mass on the Washington Mall before an expected throng of one million.

John Paul II, the former Cardinal Karol Wojytla of Krakow, Poland, already has proved to be one of the most charismatic leaders on the world stage today. The verve and vigor he has brought to his ancient role contrast sharply with the ways of most of his predecessors, almost all of them old and Italian. John Paul is neither. At 59, he's the youngest pope in more than 130 years, and the first non-Italian in nearly five centuries.

John Paul II is something of a Renaissance man -- poet, playwright, scholar, linguist, skiier, and priest. The evident difference from those who went before him has aroused worldwide curiosity. Watching him in action, both in Rome and now in Ireland, one is left with no doubt that he welcomes the curiosity, the attention. He has as sure an instinct for the crowd as the ablest of American politicians. And he's an emotional man who doesn't try to hide his feelings.

John Paul's American odyssey will take him to parishes and shrines, urban ghettoes and rural farms, the heart of large cities and the seat of the nation's political power.

All along the way the pope will address a theme that applies both to the range and diversity of American life, and the universality of the questions confronting people of all faiths, in all lands. At least that's what the people who have been helping plan his trip in the Vatican say.

Boston, for instance, the first of his stops, will be scene of his first major message. Speaking on the city's great common, so close to the physical reminders of the American Revolution commemorated in plaque and structure, he will address youth and the church -- a pertinent subject in the most influential center of American higher education.

Students are a special concern of the pope. He taught in Krakow, and developed what are said to have been close relationships with those who took his classes. In Italy, the pope has been immensely popular with young people, who credit him for the humanistic approach he has brought to the papacy.

The pope's journey next will take him to New York, where his motorcade will pass through perhaps the most blighted, economically depressed part of America -- the slums of Harlem and the South Bronx. In New York he will address the U.N. on the theme of peace and justice, before proceeding to Philadelphia Wednesday.

There his message is expected to be aimed at priests and seminarians. He then flies to the Midwest where, in Iowa, he's expected to reiterate a theme he sounded in Poland last spring -- the virtue of the small family farm. From Des Moines it is on to Chicago, and a statement on evangelicalism accompanied with a special word for Catholic bishops. Then, Saturday morning, his Boeing 747 jet takes him from Chicago to Andrews Air Force Base outside Washington.

His crowded Washington schedule calls for meeting with political leaders, as well as with President Carter and his family in the White House; a session with leaders of other faiths; a colloquy with theologians at Catholic University, and an address to nuns assembled there.

In advance of the pope's trip, a good bit of concern has been expressed -- usually privately -- by Catholics within the wide Vatican community in Rome that on his American journey John Paul may find himself restricted to what some priests call "the Catholic ghetto" -- the large Eastern Seaboard cities that are the traditional centers of church strength and influence. The worry is that this pope, with a Polish background in a communist state, has never really experienced a pluralistic society and as a consequence could be shut off from larger currents of religious thought in the broadest ecumenical sense.

Such concerns reflect the condition of a church in a time of great evolution, facing an extraordinary range of perplexing questions -- questions of dogma and practies, clerical celibacy, birth control and abortion, and a general challenge to authority no less severe than the challenge to all political authority in recent years.

The Roman Catholic church in America to which a pope finally pays personal call has changed profoundly, even though its stamp on the country has been long and significant. Catholicism had left its imprint on America well before independence was won from Britain: Catholic explorers discovered the Mississippi and gave their names and the names of great church figures to such cities as Detroit, St. Louis, and Louisville; they mapped the West and the northern frontiers, and, in the days of New France and New Spain laid claim to more than half the continent. They have left behind their culture in such cities as San Francisco, Los Angeles and New Orleans.

In the early days of the republic of Catholic presence was small -- a scant 35,000 out of a population of four million in 1780. But throughout the 19th century and into the early 20th century the Catholic population, swelled by the tide of immigrants -- Irish, Germans, Italians, and then Eastern Europeans, grew far more rapidly than the predominant Protestant. By the time of the Civil War, three of 10 Americans were Catholics, and the great growth accelerated in successive waves of European immigrants over the decades. Since the laws shutting off the great flow of immigrants in the 1920s, the church's growth has stabilized and even in recent years declined somewhat. Today, Catholics comprise some 50 million of a population close to 220 million.

Catholic assimilation has not always been a pleasant process. Catholics have been victims of suspicision, discrimination and, at times, brutality. In various periods, anti-Catholicism has proved a vibrant political force. The first half of the 19th century saw the "Know Nothings" and the American Protective Association, a claque opposed to any form of popery and papism; the 20th brought Catholics the wrath of Ku Klux Klan bigots.

And not until the last decade was a Catholic elected president. John Kennedy's presidency forever ended the idea that an American Catholic would place his political allegiance first to Rome and the Pope.

The church and the nation that John Paul II visits differ in uncalculable ways from the church feared and the nation envisioned by the John Adamses so long ago. But so too, it appears, does the current occupant of the throne of Peter differ from the popes of tradition. The chemistry between that pope and that country are certain to provide one of the more significant stories of this and perhaps many years.