Roman Catholic cardinals dressed in scarlet red robes and white ceremonial hats prayed for the election of the new pope at special mass Tuesday morning, hours before they will enter the conclave at the Sistine Chapel to cast their first ballots for the next pontiff.

The mass, called "Pro Eligendo Romano Pontefice," was held at St. Peter's Basilica and open to the public.

In his homily, Cardinal Angelo Sodano, dean of the College of Cardinal, said the role of the pope is to serve as a shepherd in the pastoral office that was first by led by Saint Peter.

He said "the last popes have been builders of so many good initiatives for people and for the international community, tirelessly promoting justice and peace."

Sodano, who is from Italy, asked cardinals and Catholics to "pray that the Lord will grant us a Pontiff who will embrace this noble mission with a generous heart. "

A group of 115 cardinals will hold the responsibility to elect the new pope. They will be scanned for bugs and mobile devices before entering the Sistine Chapel and be required to take an oath of secrecy.

Some tech-saavy cardinals posted their last words on Twitter before entering the conclave.

"Last tweet before moving to Casa Santa Martha, and mass to elect a pope," tweeted U.S. cardinal Roger Mahony. "First conclave meeting late Tuesday afternoon. Prayers needed."

Cardinals will cast their first ballots on Tuesday afternoon. If they have elected a pope by two-thirds vote, or 77 votes, then white smoke will arise from the chimney installed in the chapel. Otherwise, the world can expect to see black smoke each time after the ballots are burned.

If a consensus is not reached on the first day, the cardinals will cast four ballots a day until a new pontiff is named.

It is likely that a new pope will be announced this week, considering conclaves last on average three days, with the longest one lasting five days.

Vatican insiders say Italy's Angelo Scola and Brazil's Odilo Scherer are the two top contenders, according to Reuters.

Other front runners include Cardinal Odilo Pedro Scherer of São Paulo and Cardinal Peter Kodwo Appiah Turkson of Ghana, who would be the first black pope if elected. From the U.S., Cardinals Sean O'Malley of Boston and Timothy Dolan of New York are considered among the top choices for the papacy.

The next pope will be the 266th pontiff in the Roman Catholic Church's 2,000-year history. Within an hour after being elected, the new pope will debut before St. Peter's Square and give his first prayer.