Roman Catholic cardinals have gathered at the Vatican for preliminary meetings to discuss the next pope.

They arrived by private car, taxi and minibus at the gates of the Vatican for gatherings known as general congregations.

During the closed-door meetings they will get to know each other and decide when to start a conclave to choose a man to lead the 1.2 billion member church.

The Vatican appears to be aiming to have a new pope elected next week and officially installed several days later in time for Holy Week ceremonies, starting with Palm Sunday on 24 March.

Pope Benedict left the church in a state of shock when he announced last month that he would be the first pontiff in hundreds of years to resign instead of ruling for life.

He formally stepped down on Thursday, leaving the papacy vacant.

High on the agenda at the meetings will be the daunting challenges that will face the next pontiff, including the sexual abuse crisis that has hit the church and last year's "Vatileaks" scandal, which exposed corruption and rivalries in the Vatican's bureaucracy.

The cardinals, numbering about 150, are expected to hold one or two meetings a day.

The preliminary meetings give cardinals the chance to size up potential candidates by watching them closely in the debates.

Cardinals never reveal publicly who they prefer, but drop hints in interviews by discussing the identikit for their ideal candidate.

The most frequently mentioned quality is an ability to communicate the Catholic faith convincingly.

The Vatican seems keen to have only a week of preliminary talks so the 115 "cardinal electors" aged under 80 can enter the Sistine Chapel for the conclave next week.

The exact date for the start of the conclave has not been decided.

Most cardinals say the new pope could come from outside Europe, but it is not clear if the conclave, which has a slight majority of European cardinals, will break the long-standing tradition of choosing men only from the continent.

"We need a man of governance, by that I mean a man who is able with the people he chooses to help him in an intimate way to govern the Church," Cardinal Cormac Murphy-O'Connor, the former Archbishop of Westminster in London, told BBC radio.

No front-runner stands out but leading candidates include Peter Turkson of Ghana, Leonardo Sandri of Argentina, Austrian Christoph Schoenborn, Brazil's Odilo Scherer, Canadian Marc Ouellet and Angelo Scola, from Italy.

Roman prosecutors asked to question cardinal over abuse

Meanwhile, an Italian consumer group urged Rome prosecutors to question US Cardinal Roger Mahony, who is in the city to attend the conclave.

The Codacons group said it had asked Rome prosecutors several days ago to investigate sexual abuse the cardinal is accused of covering up in the 1980s, and to try to establish whether minors or Italian citizens were among the victims.

As archbishop of Los Angeles from 1985, Cardinal Mahony worked to send priests known to be abusers out of the state to shield them from law enforcement scrutiny, according to church files unsealed under a US court order in January.

His successor, Archbishop Jose Gomez, has removed him from all public and administrative duties, but Cardinal Mahony has made clear his intention to be among 117 cardinals allowed enter conclave.

Cardinal American and Italian Catholic activists in February petitioned Mahony to exclude himself from the conclave, saying he would taint the new pontiff with the same scandal that dogged Benedict.

An Italian abuse victims group is separately petitioning the Vatican to exclude Cardinal Domenico Calcagno from the conclave, saying the former bishop of Savona failed to report an abusive priest in his diocese to civil authorities.

The crisis involving sexual abuse of children by priests and inappropriate behaviour among adult clerics continues to haunt the church and has rarely been out of the headlines.

One elector, Cardinal Keith O'Brien, quit as Edinburgh archbishop last week and pulled out of attending the conclave because of accusations that he behaved inappropriately with priests and seminarians in the past.

He initially denied the allegations, but issued a statement yesterday apologising because "my sexual conduct has fallen below the standards expected of me as a priest, archbishop and cardinal".