As soon as he says "yes" to being pope, the new head of the Roman Catholic Church (search) will make his first major decision: He'll choose a new name.

The new pope will be free to pick from any of his 264 predecessors, use his own first name or come up with something new.

Vatican-watchers will read the choice like tea leaves offering clues to the spirit of the new papacy.

"If he chooses the name Pius XIII, it is a clear signal that he didn't like Vatican II and wants to move the church backwards," said the Rev. Thomas Reese, editor of the Jesuit weekly magazine America, referring to the conservative stance of Pope Pius XII, who died in 1958.

Taking the name John XXIV would signify "a desire to continue the Second Vatican Council," Reese said. Pius XII's successor, John XXIII, called the international gathering of prelates from 1962-65, which was credited with modernizing the church through its liberalizing reforms.

According to conclave ritual, the new pope gives his name to the cardinals while they are still gathered in the Sistine Chapel (search). The name is then revealed to the world in the "Habemus papam" ("We have a pope") announcement from the balcony of St. Peter's Basilica shortly before the new pontiff appears to give his first blessing.

In the early church, most popes kept their own names, which accounts for such archaic appellations as Adeodatus, Formosus, Hyginus and Anastasius Bibliothecarius.

In the 20th century, three popes took the name Pius, one Benedict, one Paul, and one John. In 1978, the newly elected patriarch of Venice, Albino Luciani, combined John and Paul to become the first John Paul in papal history. In deference to Luciani, who died after only 33 days in office, his successor became John Paul II.

Choosing a new name as pontiff did not become a tradition until 996, when Bruno, the first German pope, became known as Gregory V. Named after a pagan god, the 6th-century priest Mercury changed his name to John II upon becoming pope.

Over the centuries, the most popular name has been John. Twenty-three popes have taken the name of Jesus' most beloved apostle, followed by 16 Gregories, 15 Benedicts and 13 Leos.

Benedict, which comes from the Latin for "blessing," is one of a number of papal names of holy origin such as Clement ("mercy"), Innocent ("hopeful" as well as "innocent") and Pius ("pious").

The next pope could choose the name John Paul III, thus embracing the formidable legacy of his predecessor, who in 26 years on the throne of Peter traveled farther and met with more people than any other pope in the history of the church.

Such a choice would signal that the new pope is committed to continuing John Paul II's legacy, but it would also show he was responding to the "huge affection of people around the world for John Paul II," Reese said.

The one name that no pontiff has presumed to duplicate is that of Peter the Apostle, the first pope.

Although the pope is also known as the "successor of Peter," no one wants to put himself on the same level as the man who, according to church teaching, Christ himself put at the head of his flock.