Workmen began chipping into the stone floor of the sacred grottoes of St. Peter's Basilica yesterday to carve out a crypt to receive the body of Pope Paul VI, Throngs of clerics and other mourners meanwhile continued their pilgrimage to the Castel Gandolfo papal summer palace to pay homage to the dead pontiff.

The Vatican announced that the Pope's body will be brought the 15 miles to Rome today "in a simple manner" for prayers for the dead at the basilica of St. John Lateran before being moved to St. Peter's where it will lie in state under the gigantic bronze canopy created 345 years ago by Gian Lorenzo Berini.

There, hundreds of thousands of Roman Catholics from around the world are expected to file past the catafalque before a solemn requiem mass in held Saturday for Pope Paul, who died Sunday night after suffering a heart attack.

It was announced yesterday that the coffin, in a departure from tradition, will be closed for the public viewing and funeral because the sultry August temperature have begun to affect the condition of the body.

Among those visiting Castel Gandolfo yesterday were two leading "papabili," or likely papal candidates. Giovanni Cardinal Benelli, Pope Paul's former Vatican undersecretary of state, and Sergio Cardinal Pignedoli, a progressive and president of the Secretariat for Non-Christians.

The highest-ranking American in the Vatican hierarchy, John Cardinal Wright of Pittsburgh, will not be able to attend either the funeral or the election of the new pope because of surgery for muscle disorders and cataracts, a spokesman for his office said yesterday. Wright, 69, heads the Sacred Congregation of the Clergy.

Thus only eight of the 12 U.S. cardinals will be voting in the conclave. Three - Cardinals Patrick O'Byle of Washington, Lawrence Shehan of Baltimore and James McIntype of Los Angeles - are over 80 years of age and disqualified.

Throughout the day, the wooden stairs leading to the second floor papal bedroom were crowded with clerics, local residents and tourists seeking a glimpse of Pope Paul, who fro 15 years ruled for world's 600 million Roman Catholics.

In the grottoes underneath St. Peter's Basilica, thousands more Romans and tourists filed past the tombs of 17 popes, many of them hardly noticing a small chapel shrouded in black curtain, behind which masons were building a crypt under the stone floor.

The burial site, selected four years ago by Pope Paul, is about 100 feet from the flower-bedeced tomb of Pope John XIII.

The new tomb is in a chapel 19 feet long and 11 feet wide where Pope Paul often prayed, most recently on June 28, when he is said to have uttered one of his occasional musings on his own death.

Pope Paul is known to have personally approved a model of his own tomb and to have asked for a semi-abstract moisac of the resurrection of the dead, which will be installed later along with an ornate sarcophagus to replace the simple temporary crypt the workmen are now building.

As preparations for the funeral continued, the ritualistic exercise of speculating who the next pope will be.

While a half-dozen possible successors, including three Italians and three non-Italians, are mentioned most frequently, veteran Vatican observers say the election process is likely to be long and tortuous because no single strong candidate has emerged as they did in 1963 and 1939.

The most frequently mentioned papabili include Pegnedoli, Benelli and Sebastiona Cardinal Bagglo among the Italians, and among the non-Italians, Cardinals Eduardo Pironio, an Argentine of Italian descent; Franz Koenig, archbishop of Vienna, and Jo-Hannes Willebrands, arbishop of Utrecht, in the Netherlands.

The major problem facing the 115 electors of the secred college of Cardinals, according to Vatican observers, will not be in the choice of what philosophical direction the Catholic Church will head in the last quarter of the 20th century.

This conclave will represent the first time that the role of the Iuria (Vatican government) has been significantly reduced in representation, largely as a result of Pope Paul's efforts.

Three Italian cardinals most often mentioned all come from the Curia, and their foreign affairs experience often is cited as a reason for their being leading contenders, not only because of their non-provincial bearing but because they more than pastoral cardinals have frequent contact with the other electors.

But on the other hand, the body of cardinals as a whole is generally suspicious of the Curia, and in the last hundred years the only pope who had not been bishop of a clocese was Pius XII.

Of the three Italian favorites, only Benelli has pastoral experience, having been named last year by Pope Paul as archbishop of Florence.