Expressions of shock and grief from world leaders and religious figures followed the sudden death of Pope John Paul I yesterday but there were also warnings about the heavy physical burden of the arduous modern papacy.

Most of the messages that poured into the Vatican spoke of the love and joy that the dead pope had projected in his brief reign.

"We are left with the memory of a humble man who radiated joy and serenity in his engaging smile," Cardinal Basil Hume of Britain said, in a statement echoed by many others during the hours after John Paul's death was announced.

President Carter, expressing "deep sadness" at the news, said, "The warmth of his personality and his understanding of the lives of ordinary people, were evident to all. We are all made poorer by his death."

But Austrian Cardinal Franz Koenig, while praising the memory of John Paul, said his death "should serve as a warning against the physical and mental stress the pope is exposed to."

Koenig, who had been considered a possible successor to the late Pope Paul VI and is being mentioned again as a major non-Italian candidate, said "It demonstrates the need to reduce this burden to a tolerable level by dividing and delegating his responsibilities much more than has been the case until now."

Vice President Mondale, who, with Rosalynn Carter, headed the U.S. delegation to the funeral of Pope Paul VI, spoke of Pope John Paul yesterday as "a man of wisdom, simplicity and striking warmth" and said that "we are bound, now that he is gone, to pursue the hopes and expectations that he excited in us."

The most prominent Roman Catholic in the Carter administration, of Health Education, and Welfare, Joseph A. Califano Jr., said Pope John Paul "inspried us by his humility and simple pastoral manner. He will be remembered for his devotion to the high ideals of Christianity."

Canadian Prime Minister Pierre Trudeau, also a Catholic, told reporters in Montreal that "the hundreds of millions of Catholics in Canada and the world feel a bit orphaned and a bit puzzled at the ways of Providence. But I am convinced that the Church will find a solution to this."

Others, including the 85-year-old dean of the college of cardinals, express similar wonderment at the "ways of Providence."

"Providence took him away from us so suddently," Cardinal Carlo Confalonieri said. "We are all with our eyes turned upward wondering about the inscrutable designs of God."

Cardinal Joseph Hoeffner, chairman of the German conference of bishops, said John Paul's death defied human understanding and Cardinal Francois Marty, the archbishop of Paris, said: "The ways of the Lord are disconcerting to our human perspective."

Cardinal Stefan Wyszynski, the Primate of Poland, said: "It seemed that the election of this relatively young man would let the church work quietly for some longer time under his guidance. But obviously, the plans of the good Lord were different."

Although messages of condolence had come from Communist governments and leaders at the time of Pope Paul's death, there were only brief announcements of the death of John Paul by news agencies of Communist states yesterday. The different response was attributed by observers to the brief reign of John Paul and to Pope Paul's active role in building bridges to Catholics in Communist-roled countries.

In the Holy Land, Israeli President Yitzhak Navon said Pope John Paul's papacy had begun "with much promise." Lebanese President Ellias Sarkis declared a three-day national mourning period.

U.N. Secretary General Kurt Waldheim said the "example and attitude" of the late pope "will remain a lasting heritage for us all."

Queen Elizabeth II sent a message to the Vatican expressing her "deep sorrow" adding that the "humility and kindness shown by His Holiness will remain a lasting and inspring memory."

French President Valery Giscard d'Estaing said that the world would remember Pope John Paul for his enlightening smile and his pastoral simplicity.

Most Latin American countries decreed periods of mourning. A major meeting of Latin American bishops, set for Puebla, Mexico, on Oct. 12, was indefinitely postponed.

World religious figures spoke affectionately of the pontiff who, before he became pope, had been active in ecumenical activities.

Donald Coggan, the Anglican archbishop of Canterbury, said the pope's death was a "great loss to the church and to the world." Archbishop Seraphim, the Greek Orthodox primate, said in Athens that "we appreciate the pure sentiment which he expressed."

In Geneva, a statement issued by leaders of the World Council of Churches, said Pope John Paul would be remembered "above all for his utter commitment to Christ and his church."

Billy Graham, the American evangelist, said in Sweden, where he is visiting, that the late pope "seemed a pastoral man who believed in the need for evangelism."

In a discordant note, Abbot Francois Coache, a follower of rebel Archbishop Marcel Levebvre, said, "If the Almighty took away John Paul I after one month it is because God did not want him to reign" and "did not want to ratify the choice of the cardinals" who elected him.