Pope John Paul I, who died in the Vatican Thursday night after a heart attack at the age of 65, was widely regarded as a man whose openness and simplicity could ease the pressures and conflict within the Roman Catholic Church.

He once described himself as "a little man accustomed to littel things and to silence." The 34 days in which he served as the 262rd successor to St. Peter and leader of the world's 600 million Roman Catholics were marked by gestures and innovatioins - even surprises - that seemed to bear out not only his simplicity but also his awareness of his churchs problems.

The first of the surprises - his election to succeed Pope PauL VI, who died Aug. 6 - was not of his doing. It was the work of the College of Cardinals. The new pope had been a Ibino Luciani, a cardinal and the Patriarch of Venice.

He had spent his life in the church in pastoral duties and as a teacher. He had never been assigned to the Curis, the church's powerful central office, and his experience in foreign affairs was nonexistent.

The second surprise was the choice of the name by which he wished to be known: John for Pope John XXIII, the warm and hearty innovator who ushered in a period of change by convening the Second Vatican Council, and Paul for Pope Paul, the austere and remote churchman who sought to guide the changes while still maintaining the church's traditional opposition to artificial means of birth-control, and abortion and divorce.

John Paul set the tone of his papacy on Aug. 27, the day after his election. Speaking to a cheering crowd gathered in St. Peter's Square, he said: TR FOR DD TWO-

"Obviously, I have not the wisdom of the heart of Pope John nor the training and culture of Pope Paul," he said. "But I am here in their place, so I have to try and serve the church. I hope you will help me with your prayers."

Then he told a story about his thoughts during the conclave of cardinals that had made him pope - and in doing so he broke a tradition by which all who take part in a papal election keep a vow of silence about the process.

"Yesterday morning I came to the Sistine Chapel to vote tranquilly," the new pope said. "But I never imagined what was to follow. As soon as the danger (of being elected) began for me, two colleagues near me reassured me with words of courage.

"One said to me, 'Courage. If God gives you a burden, He also gives you help to carry it.' And another colleague said, 'Don't worry. In all the world there are so many people who pray for the new pope.'"

John Paul was apparently elected on the third ballot taken by the cardinals meeting in conclave. It was one of the shortest conclaves in the church's history.

Within the first hours of his papacy, John Paul gave a televised address in which he sent greetings to the poor and stated the church's long-held views on contraception and related matters.

Families, he said, should be "defended from the destructive attitude of sheer pleasure-seeking that snuffs out life."

Concerning the poor, he said: "We want to send a special greeting to all those who are suffering at this moment.To the sick, to prisoners, to the exiled, to the persecuted; to those who have no work or encounter difficulties in the hard struggle for life; to those who suffer for the constructions placed against their Catholic faith, who are unable to freely practice this faith without losing their basic rights as free men and citizens."

John Paul became pope the moment he accepted his election. His formal coronation occurred on Sunday, Sept. 3, and was televised around the world. For all its magnificence, the ceremony was less elaborate than tradition seemed to dictate. Many sought further clues to the course of John Paul's papacy in the relative simplicity.

The ceremony was conducted outdoors. The alter was a simple wooden affair. This pope foreswore the portable throne carried by footmen used by many of his predecessors. Instead, he walked to the ceremony. He also foreswore use of the triple crown, the papal tiara, and the use of a canopy over his throne.

In his homily, John Paul called on the world for "justice, brotherhood . . . and hope."

It was a theme to which he returned several days later in an address to the diplomatic corps in the Vatican.

"These principles are respect for one's neighbor, for his life and for his spiritual and social progress, patience and the desire for reconciliation in the fragile building up of peace," the pope said.

John Paul often was described as a "moderate conservative" on the issues confronting the church. He opposed the worker-priest movement in which priests entered factories to be closer to their flocks. He opposed communion. As bishop and cardinal, he disciplined priests who dissented from Pope Paul's pronouncements against abortion and divorce.

But on his own role in the Second Vatican Council, in the course of which he seems to have made little impression on his fellow bishops, he said, "The part that caused me more problems was that on religious liberty."

This was a reference to the council's decree sanctioning the full rights of religions other than Roman Catholicism. The Catholic Church previously had held that only Roman Catholicism had such liberties and protections. This view had long been espoused by Alfredo Cardinal Ottaviani, the head of the Vatican's Holy Office and a noted conservative in curial affairs.

"For years I had been teaching Ottaviani's theories about law, according to which only the true religion has rights," John Paul said. "I convinced myself we were wrong."

John Paul indicated that he would continue the ecumenism that Pope Paul had pursued so carefully. Like his predecessor, he also indicated that while he would share some power with the bishops of the church, he would keep final decisions to himself.

Albino Luciani was born in the village of Forno di Canale in the Italian Dolomites in northern Italy on Oct. 12, 1912. His father was a socialist who spent some years as an itinerant worker in Switzerland. The elder Luciani later got a job in one of the lands in the lagoon of Venice. The future pope once described his motor, who came from a peasant family, as "strong and devout."

The young Luciani entered a seminary and was ordained on July 7, 1936. During his student days he would return home to help with the farming in the summer. After his ordination and studies at the Gregorian University in Rome, where he took a degree in dogmatic theology, he returned to his village - which has been called Canale d'Agordo since 1964 - to take up the duties of a parish priest.

From 1937 to 1947, he was deputy director of the seminary at Belluno, where he himself had been a student. In 1948, he became a deputy to the bishop of Belluno. Ten years later, Pope John XXIII made him bishop of Vittorio Veneto, and in that post he sometimes made pastoral visits on a bicycle.

In 1969, Pope Paul named him patriarch and archbishop of Venice. He remained there until he assumed the papacy, becoming the third bishop of Venice to become pope in this century (after Pius X in 1903 and John XXIII in 1958).

It was during his years in Venice that John Paul, who contributed numerous articles to the press on church affairs, wrote a book called "Illustrissimi." It was a collection of open letters addressed to famous figures of the past, and it has become a best-seller since its author became pope.

In it is a letter to Charles Dickens, in which John Paul wrote: "We are in one boat full of people . . . If we don't want to encounter serious turmoil, the rule is this: all for one and one for all . . . The whole world is a poorhouse, and has such need of God."

Another is addressed to Mark Twain, a favorite of John Paul, and it defines the author's view of himself as a bishop. After remarking that some of his superiors were "scandalized" because he used Mark Twain Stories in his sermon, John Paul said:

"Perhaps one should explain to them that bishops are as varied as books are. Some resemble eagles who glide majestically at high levels. Others are nightingales who sing the praises of the Lord in a marvelous way. Others, instead, are poor wrens on the lowest bough of the ecclesiastical tree who only squeak, seeking to offer some small thought regarding the great themes. I belong to the last category."