Pope John paul I reinstated the Vatican hierarchy of his predecessor yesterday in his first major administrative action as head of the Roman Catholic Church.

Pope John Paul, who began his pontificate with a self-effacing address to hundreds of thousands of persons in St. Peter's Square Sunday, is apparently planning a simple enthronement ceremony next Sunday instead of the usual elaborate coronation rites.

Vatican Radio said the installation will be "a solemn mass for the start of the ministry of the supreme pastor" and will be held outdoors in St. Peter's Square, as was the precedent-setting coronation of John Paul's predecessor, Pope Paul VI.

Vatican officials said the decision means that Pope John Paul does not want to receive the papal triple crown of silver and gold. Nor did Paul VI. He sold his crown and gave the money to the poor.

There has not been an enthronement ceremony in living memory and protocol experts were uncertain of many details. "The decision has thrown the ceremonial department inot chaso," one source said.

A Vatican announcement said the new pope is continuing in office the heads of the nine sacred congregations, the departments that administer the affairs of the Church.

John Paul also reappointed Pope Paul's secretary of state, Jean Cardinal Villot, 72, of France, the late pontiff's most trusted aide. As papal chamberlain between the death of Pope Paul Aug. 6 and the election of John Paul last Saturday, Villot was interim head of the Vatican Curia, the church's highest administrative council.

John Paul I also retained Archbishop Agostino Cassaroli as secretary of the Council for Public Affairs, the Vatican's Foreign ministry.

The reappointments were expected. The new pontiff has had little experience with the Curia and it is believed he wants to learn about the Vatican's governing machinery before making any major changes.

The Curia includes such offices as the powerful Congregation of Bishops, headed by Sebastiano Cardinal Baggio, which controls appointments of bishops around the world.

Another important post, the Congregation for the Doctrine of the Faith, which acts as watchdog over church doctrine, is headed by Franjo Cardinal Seper, a 72-year-old Yugoslav.

The Congregation for the Clergy is headed by John Cardinal Wright, 69, Boston, the hightest-ranking American in the Curia. Wright did not participate in the conclave that elected Pope John Paul because he is recuperating from eye surgery in Massachusetts.