VATICAN CITY, - Pope Benedict celebrates his inaugural Mass in St. Peter's Square on Sunday, returning for his first public sermon as Pontiff to the spot where he conducted John Paul's huge funeral two weeks ago.

Presidents and prime ministers, leaders of other religions and about half a million pilgrims, were expected to pack the square and surrounding streets to see the 78-year-old leader of the Roman Catholic Church receive the symbols of his authority.

They are the Fisherman's Ring, a gold signet ring showing St. Peter in a boat fishing, and a white wool stole decorated with six black crosses known as the pallium.

Many in the crowd will be from the Pope's native Germany. Groups waving German and Bavarian flags began arriving on Saturday and more were due at dawn after all-night bus trips.

"It's something very special that the Pope comes from our homeland," Kathrin Brauner, a high school student from Cologne, said on the square after a 19-hour bus ride to Rome.

Fewer world leaders were due at the Mass than at John Paul's funeral, which with 2,500 dignitaries resembled a summit of the world's powerful, but the attendance list for the last main event in the papal transition is still long.

Chancellor Gerhard Schroeder and President Horst Koehler are heading the German delegation. The U.S. group is led by Florida Gov. Jeb Bush, brother of U.S. President George W. Bush and a convert to Roman Catholicism.

The guest list includes Spain's King Juan Carlos and Archbishop of Canterbury Rowan Williams, the spiritual head of the Anglican Communion.

Also present will be Benedict's priest brother Georg, 81. The Mass will be in Latin with prayers in languages from German to Arabic and Chinese.

After the Mass, Benedict was expected to be driven around the Square in an open car, not the "popemobile" that would ferry the invalid John Paul around at public appearances.

GROWING INTO NEW ROLE

The shy Pope, who as Cardinal Joseph Ratzinger was John Paul's top doctrinal overseer, has been slowly growing more comfortable in his new role since being elected in a secret conclave last Tuesday.

He displayed his linguistic skills at a special audience for journalists on Saturday, thanking them in fluent Italian, English, French and German for bringing the historic events of recent weeks to readers and viewers around the world.

The death of John Paul, his funeral and the conclave that elected Benedict was a media event like no other in recent history, with billions of viewers tuning in across the globe.

"In my own name, and especially on behalf of Catholics living far from Rome who were able to participate in these stirring moments for our faith that were taking place, I thank you for all you have done," Benedict said.

Attention during Sunday's two-hour rite will focus on his homily.

As the Vatican's doctrinal watchdog, Ratzinger upset Protestants, Buddhists and Hindus with sharp criticisms of their faiths. But his first address as Pope stressed the need for inter-faith dialogue.

Rome will shut off its airspace for the Mass and has anti-aircraft missiles and a NATO plane guarding against attack.

More than 1,000 volunteers have been drafted in to marshal the crowds, including some from a German-speaking area of northern Italy to help pilgrims from the Pope's homeland coming to see their first compatriot in centuries be installed as Pope.

The Pope was due to meet visiting dignitaries later on Sunday and hold an audience for German pilgrims on Monday.