Pope John Paul I will have no coronation or enthronement, but instead will consecrate his pontificate by simply celebrating mass Sunday in St. Peter's Square.

The Vatican announced yesterday that the new pope, formerly Cardinal Albino Luciani, archbishop of Venice, will celebrate the solemn mass at 6 p.m. (noon EDT) "to mark the beginning of his ministry as supreme pastor."

Pope John Paul, 65, will walk from St. Peter's Basilica to the open-air altar on the stairs outside instead of being borne by attendants on a portable throne, as has been customary in the past.

His decision to break away from the pomp and splendor of a formal coronation was in keeping with the relaxed style he displayed as patriarch of Venice, with his long pastoral experience, and with the self-effacing sermon he preached in St. Peter's Square on Sunday, the day after he became pope.

He was elected Saturday by the Sacred College of Cardinals, called into conclave to name a successor to Pope Paul VI, who died Aug. 6.

The mass Sunday will replace an ancient coronation ceremony that opened the reigns of at least 107 of John Paul's 262 predecessors. In these rites, a gold and silver tripple crown was placed on the pope's head with the words: "Receive this tiara adorned with three crowns andknow that your are the father of princes and kings, guide of the world and vicar upon earth of Jesus Christ our savior."

The last pope not to be crowned was Urban VII, who reigned only 12 days in 1590 and did not live to set the date for his coronation. Pope Paul Vi had his own triple crown sold after his coronation and used the proceeds to help the poor.

Msgr. Orazio Cocchetti, of the Vatican's office for pontifical ceremonies, told reporters that another installation rite to be eliminated is the flax-burning ceremony by which the new pope is reminded of the fleeting character of wordly glory.

In this ritual, a priest carries a cane topped with burning flax to the pontiff and chants three times in Latin: "Holy Father, so passes the glory of the world."

"It was dropped to make for a simpler rite overall," Cocchetti said.

The White House announced yesterday that Vice President Mondale will represent President Carter at the inaugural ceremonies. Mondale will be accompanied by his wife Joan, their son William, and "a delegation of distinguished Americans," the announcement said.

Also among the spectators will be Silvio Luciani, 78, of Marysville, Mich., a retired bricklayer who has been fond of telling friends and relatives that his younger first cousin, the patriarch of Venice, would be pope someday.