Black smoke poured from the Sistine Chapel's chimney in the Vatican (search) Monday evening, signaling that the cardinals meeting in secret inside have not yet chosen the next pope to lead the world's 1.1 billion Roman Catholics.

The black smoke meant the 115 voting cardinal "princes" of the church would retire for the night and return to the chapel Tuesday morning for more balloting in their search for a successor to Pope John Paul II. If two morning ballots fail to produce a pope, the cardinals could hold two more votes Tuesday afternoon.

Some 40,000 people who packed St. Peter's Square (search) to stare at the stovepipe jutting from the chapel roof shouted, "It's black! It's black!" and snapped photos with their cell phones.

Monday was the first day of what could be a long yet historic process to elect the next pope, or it could all wrap up in the next day or two. Over the past 100 years, conclaves have taken between two and five days to select a pope; the average is about three days.

"I slept well, and now my ideas are clear," French Cardinal Paul Poupard said as he headed into the Mass on Monday. "I have realized the seriousness of the election. The Holy Spirit will do the rest."

Representing 52 countries, the cardinals earlier celebrated a midmorning Mass at St. Peter's Basilica (search). Clad in crimson vestments and caps, thet then walked slowly from the Apostolic Palace to sequester themselves inside the Sistine Chapel (search) decorated with frescoes by Michelangelo.

Inside the chapel, seated atop a false floor hiding electronic jamming devices designed to thwart eavesdroppers, the cardinals read out an oath of secrecy led by Cardinal Joseph Ratzinger (search), who stood before a large crucifix adorned with a golden Jesus. One by one, they filed up to a Book of the Gospels, placed their right hands on it and pronounced a second oath to keep their deliberations secret.

Ratzinger's admonition read, in part: "In a particular way, we promise and swear to observe with the greatest fidelity and with all persons, clerical or lay, secrecy regarding everything that in any way relates to the election of the Roman Pontiff and regarding what occurs in the place of the election, directly or indirectly related to the results of the voting; we promise and swear not to break this secret in any way ..."

The cardinals were to hear a meditation before deciding whether to take their first vote or wait until Tuesday.

Smoke in the Sky

In his homily Monday morning, Ratzinger — a powerful Vatican official from Germany often mentioned as a leading candidate to become the next pope — spoke in unusually blunt terms against "a dictatorship of relativism" — the ideology that there are no absolute truths.

"Having a clear faith, based on the creed of the church, is often labeled today as a fundamentalism," Ratzinger said. "Whereas relativism, which is letting oneself be tossed and 'swept along by every wind of teaching,' looks like the only attitude acceptable to today's standards.

"We are moving toward a dictatorship of relativism which does not recognize anything as for certain and which has as its highest goal one's own ego and one's own desires."

Ratzinger drew applause as he asked God to give the church a "a pastor according to his own heart, a pastor who guides us to knowledge in Christ, to his love and to true joy."

The cardinals chanted the Litany of the Saints as they made the short walk to the chapel, led by altar servers carrying two long, lit white candles and a metal crucifix.

In a procession carried live on Italian television, they walked past a pair of Swiss Guards in red plumed hats standing at attention at the entrance to the chapel and took two steps into the voting area.

Ratzinger entered the chapel last -- an honor bestowed upon the dean of the College of Cardinals.

Before the procession, Ratzinger asked for prayers from the church that a pastor fit to lead all of Christ's flock would be elected.

"May the Lord lead our steps on the path of truth, so that through the intercession of the blessed Virgin Mary, the Apostles St. Peter and St. Paul, and of all the saints, we may always do that which is pleasing to him," he said in Latin.

The cardinals took their assigned places behind their name placards, with a copy of the conclave ritual on their desks. They then placed their red, three-cornered square birettas on the tables, leaving only their crimson skullcaps on their heads.

Thousands of pilgrims and tourists were expected to converge on St. Peter's Square to watch the chapel chimney for the white smoke that ultimately will tell the world that the church's 265th pontiff has been elected. The famous stove in the chapel also will bellow black smoke to signal any inconclusive round of voting.

Young American men studying theology in Rome waved a giant U.S. flag as they emerged from the Mass.

"We like Ratzinger," said Nicholas Lebish, who studies at Lateran University. "He is both conservative and compassionate, and he knows all about church teaching."

Although the conclave could last for days, a pope could be chosen as early as Monday afternoon if the red-capped prelates opt to begin casting ballots after their solemn procession from the Vatican's Apostolic Palace to the chapel.

If they decide to hold off a day, they will hold four rounds of voting — two in the morning, two in the afternoon — on Tuesday and every day until a candidate gets two-thirds support: 77 votes. If they remain deadlocked late in the second week of voting, they can vote to change the rules so a winner can be elected with a simple majority: 58 votes.

Vatican spokesman Joaquin Navarro-Valls said smoke from burned ballot papers enhanced by special chemicals likely could be seen at around noon and around 7 p.m. on each day of voting by the cardinal electors, all of whom are under age 80. At some point soon after the new pope is chosen, the Vatican also will ring bells.

The Prospects

There are no clear favorites in sight to take over for Pope John Paul II, making the question of papal succession as unpredictable as any in recent history. The cardinals must decide whether to follow John Paul with another non-Italian or hand the papacy back to its traditional caretakers.

When the College of Cardinals selected him in 1978, John Paul — then a Polish cardinal himself — became the first non-Italian pontiff in 455 years and the first from Poland.

Through his choice of cardinals, John Paul II increased the odds that one of his men will be the next leader of the Catholic Church. He chose many of them in his image as a conservative interested in social justice.

Cardinal Angelo Scola, the patriarch of Venice, is seen as a possible surprise contender. He was among 30 new cardinals to be installed in October of 2003. He is considered to be a conservative and in 1995 was assigned to head the Pontifical Institute on Marriage and the Family, which has promoted the pope's conservative views on sexuality, abortion and marriage.

Cardinal Dionigi Tettamanzi — seen as Italy's best hope to regain the papacy — was ordained a priest in 1957 by Cardinal Giovanni Battista Montini, who would go on to become Pope Paul VI. He has been praised in the Vatican's appointment announcement for the "clarity and depth" of his thought in his theological teaching and for his loyalty to Church teaching.

Another Italian candidate is Cardinal Giovanni Battista Re, a conservative who became close to Pope John Paul II as the Vatican's under secretary of state.

Meanwhile, Cardinal Francis Arinze is the only black cardinal who is spoken of as a possible successor. A native Nigerian who is currently based in Rome, Arinze is a popular figure known for his affability. If elected, Arinze would be the first black pope in more than 1,500 years and his appointment could prove a huge boost to Catholicism in Africa and amongst U.S. black communities.

Cardinal Carlo Maria Martini, a prominent Jesuit and retired archbishop of Milan, could gather enough votes to block the powerful and respected Ratzinger and allow another cardinal to emerge. Ratzinger wields much influence in the Vatican and is one of the world's most visible cardinals. He was one of John Paul's closest aides and the eyes of the world were on him when he led the late pope's funeral mass.

Ratzinger is favored by those who want assurances the conservative policies of John Paul — opposition to contraception, women priests and any loosening of mandatory celibacy for priests of the Western church — won't be relaxed, according to a prelate. But the German's age and his recent ill health could be a deterrent for electors seeking a younger pontiff.

Other contenders are Cardinal Christoph Schoenborn of Czechoslovakia, the liberal Godfried Danneels of Belgium, Patriarch of Lisbon Cardinal Jose da Cruz Policarpo of Portugal, Cardinal Oscar Rodriguez Maradiaga of Honduras, Mexican conservative Cardinal Norberto Carrera Rivera, Brazilian progressive Cardinal Claudio Hummes and the Italian-speaking Jesuit Cardinal Jorge Bergoglio of Buenos Aires.

Cloaked in Secrecy

On Sunday, the cardinals moved into the super-secure Domus Sanctae Marthae, the $20 million hotel that John Paul had constructed inside Vatican City so the cardinals could rest in comfort in private rooms between voting sessions.

Conspicuously missing from their quarters were cell phones, newspapers, radios, TVs and Internet connections — all banned in new rules laid down by John Paul II to minimize the chances of news influencing their secret deliberations and to prevent leaks to the outside world. The Vatican's security squad swept the chapel for listening devices, and cooks, maids, elevator operators and drivers were sworn to secrecy. Excommunication is a possible punishment for any indiscretions.

The prelates agreed after John Paul's funeral not to talk publicly about the process, but the world's news media have been rife with speculation centering on about two dozen candidates considered "papabile," Italian for "pope material."

Among the issues sure to figure prominently in the conclave: containing the priest sex-abuse scandals that have cost the church millions in settlements in the United States; coping with a chronic shortage of priests and nuns in the West; halting the stream of people leaving a church whose teachings they no longer find relevant; and improving dialogue with the Islamic world.

"We are praying together with the church for everything to get better," said Sister Annonciata, 42, a Rwandan nun from the Little Sisters of Jesus order who was in Vatican City on Monday.

Cardinal Salvatore Pappalardo, an Italian who at 86 is too old to vote, told Italian state radio Sunday he was confident the conclave would be guided to the right man.

"Providence sends a pope for every era," he said.

The Associated Press contributed to this report.