The College of Cardinals will convene Tuesday to begin the formal process of selecting a new pope to lead the world’s 1.2 billion Catholics, the Vatican announced Friday.

In their eighth general congregation, or pre-conclave meeting, the cardinals voted to start the conclave Tuesday afternoon, after a morning “pro eligendo Romano Pontifice” Mass in St. Peter’s Basilica.

The cardinals will convene inside the Sistine Chapel, and they are sworn to secrecy and barred from contact with the outside world until their deliberations are complete. Voting begins the first afternoon. If no papal candidate receives the required two-thirds of the votes, the ballot is repeated twice each morning and afternoon. If, after the third day, no pope is elected, a one-day break for prayer is permitted. Since the early 20th century, no conclave has lasted more than five days.

In his daily update Friday with the Catholic Channel on Sirius XM, Cardinal Timothy Dolan of New York said he thought the cardinals by Saturday could complete their pre-conclave sessions — in which they listen to discussions of the challenges facing the church in individual countries and take the measure of the men among them who could be pope.

“That’s certainly not my decision. That’s to the congregation,” Dolan said. “But I’m sensing, perhaps, I’m sensing a hope that we may be able to wrap up the meetings by tomorrow.”

From the moment Benedict XVI announced his retirement, speculation started to swirl over who will replace him as Pope. Ben Connors gives us a look at a few of the prospects. (The Fold/The Washington Post)

The picking of the date puts to rest one of the first questions of the selection process and turns attention to more interesting mysteries: Will the Italians, who dominated the papacy for more than four centuries before the ascent of Poland’s John Paul II in 1978, reclaim the throne, or will another non-Italian pope be selected? (Benedict XVI is German.)

Will the 266th pontiff be the first from the so-called New World, either from South America, where the church’s 200 million faithful are courted in a lively religious marketplace, or from North America, where American and Canadian candidates are seen as surprisingly strong? Or will the church look to Africa, where it is gaining strength, or Asia?

And finally, who will emerge victorious from the power struggles inside the college: Prelates aligned with the church bureaucracy? Or the outsiders who hope to reform it?

On Sunday, many of the cardinals are expected to visit their titular churches in Rome, offering what could be a last glimpse of the prelates before they enter the conclave (from the Latin “with a key”). Before they begin a Vatican lockdown, they will spend these last days hammering out alliances, gravitating toward candidates or working to peel off supporters from other papal contenders.

Once inside the Sistine Chapel, the Vatican’s chamberlain — a position filled by Benedict’s former second in command, the embattled Cardinal Tarcisio Bertone — will declare “extra omnes.” At that moment, everyone without a vote exits, leaving the cardinals alone with Michelangelo’s frescoes and ballots reading “Eligo in summum pontificem” (“I elect as supreme pontiff”) across the top.

The most senior cardinals go first, holding the folded ballot up for their colleagues to see as they kneel at the altar, pray and declare, “My vote is given to the one who before God I think should be elected.” One by one, the cardinals will drop the papers into a silver and gilded bronze urn — recently revealed to the Vatican press corps in a short video — and an official sews the ballots together with a thread tied to a needle that pierces through the word “Eligo.”

Eventually, one of those ballot counts next week could cross the threshold of 77 votes for one of the cardinals, prompting a puff of white smoke (thanks to the addition of some chemicals) from the Sistine Chapel’s chimney when the ballots are burned. A cardinal would then come to the balcony of St. Peter’s and introduce the new pope, cloaked in white, with a cry of “Habemus Papam.”

The cardinals voted early Friday to accept the absence from the conclave of two voting-age cardinals who had said they would not attend. The first, a cardinal from Jakarta, Indonesia, asked to be excused because of health problems. The second is Cardinal Keith O’Brien of Scotland, who in recent weeks was accused of and admitted to inappropriate sexual behavior toward priests. When O’Brien announced his resignation as head of the Catholic Church in Scotland last month, he said he would not participate in the conclave.

The Feb. 28 abdication of Benedict XVI, now known as pope emeritus, injected an unusual dose of uncertainty into a process traditionally governed by funeral rituals, homilies and masses.

Benedict was the first pope in nearly 600 years not to die in office. Usually, the conclave to select a new pope begins after a 15-day period of mourning the previous pope’s death.

In the absence of funeral rites, public attention in recent days has focused on matters of logistics and media access. The Vatican spent much of the past week answering questions about the vagaries of Benedict’s eleventh-hour amendment to an apostolic constitution and whether all voting-age cardinals needed to be in attendance before the college could decide on a conclave start date. (Cardinals who are younger than 80 at the time the papacy became vacant are eligible to vote. The 115th and final voting-age cardinal to participate in the election, a Vietnamese prelate, arrived Thursday.)

The start date of this conclave had become a source of debate among cardinals, with some factions believing they would benefit from an earlier election and others pushing for a longer preliminary period that would allow more time for less-familiar candidates to emerge.

Media restrictions imposed by the College of Cardinals put a sudden and unexpected end to daily news conferences that were being held by American cardinals, drawing media attention to the Vatican’s censorship rather than the major themes the cardinals have been discussing.

On Friday morning, 18 more cardinals spoke at the closed meeting, bringing the total who have addressed the college to more than 100. The Rev. Federico Lombardi, a Vatican spokesman, said they discussed interreligious dialogue, bioethics, justice in the world and the importance of positive announcement of the Gospel.

During the meeting, they also learned of an “adopt a cardinal” Web site where 220,000 people have logged on to pray for one of the 115 voting cardinals.

Angelo Sodano, the dean of the College of Cardinals, who is more than 80 years old and therefore cannot enter or vote in the conclave, said that he hoped the Web site was for all of the cardinals, not just the electors.

During Friday’s news conference, Lombardi showed a film of the hotel on Vatican grounds where the cardinals will stay during the election. “We are getting close to the conclave,” he said.