With cardinals of the Roman Catholic Church converging on Rome, the Vatican announced yesterday that Pope John Paul I would be buried Wednesday after an outdoor funeral in St. Peter's Square here and that the secret conclave to elect his successor will begin 10 days later.

The Oct. 14 date for the conclave is only one day after the earliest date allowed by Vatican regulations.

The announcement came as the body of the pope was moved in a simple procession from the papal apartments into St. Peter's Basilica after being borne through a crowd of thousands of mourners gathered in the 17th century square.

The body, which will lie in state there until the funeral, will be buried in the crypt of the basilica where John Paul's modern predecessors are also interred.

Vice President Mondale will head the U.S. deleation to the funeral.

The 29 members of the Sacred College of Cardinals who were already in Rome met yesterday to set the date of the funeral. They also scheduled the secret conclave to open Oct. 14 amid a new round of speculation about John Paul's successor.

The analysts, who failed even to mention Cardinal Albino Lucianai, who became John Paul, as a possibility, were being extra-cautious this time. Only one Italian newspaper had named him, as one of the serious papabila possible popes.

It was noted, however, that if the cardinals follow the same reasoning that they used in August and seek in Italian with experience as head of a large diocese, that would narrow the field to Cardinal Salvatore Pappalarno 60, archbishop of Palermo, Sicily; Cardinal Giovanni Benelli, 57, archbishop of Florence; and Cardinal Ugo Poletti, 64, the vicar of Rome.

The other Italian cardinal-archbishops from Bolognia, Naples, Milan and Genoa are in or near their seventies. After the experience of John Paul's brief papancy, the choice of an older man is considered unlikely.

Benelli of Florence may, on the other hand, be too Young.

Another candidate who may be considered too young is Cardinal Eduardo Pironio, 57, born and reared in Argentina of Italian parents. Now a member of the Vatican Curis, he has served as a bishop in Argentina.He could be a logical choice to bridge the gap between the "Italians" and the "foreigners".

The faithful continued to come to pay their respects to John Paul. The Italian news agency estimated that 250,000 persons stood under the warm Roman sun in the long, snaking line inside the columns of the oval-shaped St. Peter's Square to file past the body.

There were few scenes of grief.

Many of the men wore short-sleeved sports shirts. There were large numbers of tourists with cameras.

Pietro Romani, a city street-sweeper, said of John Paul. "He was too simple a man to bear up under so much responsibility." But Paolo Moro, a tax driver compared the last pope favorably to his predecessor Paul VI: "He was a good Christian, a poor people's pope. Montini was good but he left us feeling somewhat inadequate. Luciani gave us confidence."

The pope's reign may nevertheless prove to have some lasting effect on the style of the Vatican.

For the first time in memory, the Vatican newspaper, the journalistically conservative Observatore Romano, ran a man-in-the-street story quoting laymen by name on their reaction to the pope's death.

Most of those interviewed, including a desk clerk and a Venezuelan admiral, seem to have been questioned in the lobby of the Grand Hotel.

Only a few weeks ago Observatore was refusing to print the new pope's off-the-cuff remarks and changing his simple "I" in speeches in the traditional imperial "We".

The crowd in St. Peter's Square to see the transfer of the body was estimated at 60,000 - about half the number the square can hold.