* Abuse victims say Pope Benedict's apologies fell short
* Demands for child protection for millions in Church care
* Scandal plagues conclave as cardinals called not to attend
* Next pope will take up challenge that undermined Church (Updates details, edits)
By Naomi O'Leary
VATICAN CITY, March 7 (Reuters) - Colm O'Gorman was 14 years old when Father Sean Fortune arrived unannounced at his parents' house in a small town in southern Ireland. The priest was given tea and a seat by the fire, and asked the teenager to help set up a youth group.
"I was 14, and very eager and hungry to be out in the world, involved in things, doing things, making a difference. And that's what he exploited," said O'Gorman, now 46 and the executive director of Amnesty International in Ireland.
The abuse that followed, culminating in Fortune's repeated rape of the boy, was part of one of the greatest scandals ever to hit the Catholic Church, damaging the curtailed papacy of Pope Benedict and posing a huge challenge to his successor.
The scandal has haunted the Church for a decade in the United States and several European countries, and ranks as a top concern for cardinals preparing to elect a new pope.
Monsignor Charles Scicluna, until last October the Vatican's chief prosecutor of these cases, said abuse harmed not only the body "but the soul and the faith of believers.
"This is a battle that we cannot afford to lose," he said in an Italian television interview last week.
NO QUESTIONS ASKED
O'Gorman fell victim to one of Ireland's most notorious molesters, a popular but manipulative priest who led a double life as a serial abuser. Eventually, unlike the vast majority of abusive priests, the police began investigating.
While many predator priests had only one or a few victims, Fortune was charged with 66 counts of assault and rape of boys. He killed himself in 1999 when his case was being brought to trial.
No questions were asked when Fortune took O'Gorman to his isolated house for the weekend. Such was the Church's power in Ireland at that time, no one would question a priest.
That was the first time Fortune sexually assaulted O'Gorman. Driving him back to his parents the next day, the priest stopped the car around the corner from the teenager's home.
"There were no words that I had that could explain what had happened, and I was terrified," O'Gorman recalls. "He said to me: 'I'm worried about you, you have a problem. Either I can tell your parents, or you can come back down to me again.'"
"He kept coming and taking me away, for nearly three years."
Fortune's attacks became increasingly violent and escalated to rape. O'Gorman, depressed and suicidal, finally fled his hometown. He became homeless on the streets of Dublin.
It took a decade for O'Gorman to re-establish contact with his family and explain what had happened. With their support, he made a report to the Irish police in 1995.
"Within weeks, I heard back from the detective who had started the case that they had found another five victims," O'Gorman said.
The investigation revealed a bully priest who manipulated and abused people wherever he went, and a Church hierarchy that, after receiving complaints about him, moved him on to places where he found new victims: a pattern that recurred in its handling of abuse cases worldwide.
After Fortune's death, and although there was little legal precedent, O'Gorman took a civil suit against the Diocese of Ferns and Pope John Paul in 1998. In it he cited evidence that Fortune's crimes were well known but that the Church did nothing to limit his access to children.
The diocese apologised in 2003 and paid O'Gorman 300,000 euros ($389,500) in compensation.
In a dramatic illustration of the loss of faith in the Church across the developed world, Ireland - where Catholicism was written into the constitution and had enormous influence throughout the 20th century - closed its embassy to the Holy See in 2011 as relations hit an all-time low.
The sexual-abuse crisis and its continuing repercussions on the Church was likely one of the difficulties Benedict referred to when he became the first pontiff in centuries to abdicate, saying he no longer had the strength to continue.
In 2001, as the scandals mounted, then-Cardinal Joseph Ratzinger took responsibility for abuse cases at the Vatican. As the chief doctrinal watchdog, he regularly read the details of case after case of abuse and formulated responses to them.
"There was no one in the Church hierarchy who was better positioned to make a real difference than Pope Benedict," David Clohessy, director of the U.S.-based Survivors Network of those Abused by Priests said last week. "He had both the power and the knowledge."
FILTH IN THE CHURCH
Shortly before his election in 2005, Ratzinger gave a now-famous address in which he lamented "filth" in the Church, seen as an indicator he would take a tougher line if made pope.
After his election, as the scandal was gaining more publicity, Benedict met abuse victims in Germany, the United States, Australia, Malta and Britain, and barred two high-profile former Vatican favourites suspected of abuse from office.
The barring from public ministry of charismatic Italian priest Gino Burresi and Marcial Maciel, the Mexican founder of the Legionaries of Christ religious order who was a favourite of the late Pope John Paul, marked a watershed, showing the Church was finally acting against abuse.
Victims' groups say that the Vatican had a policy of not reporting abusive priests to secular authorities, citing evidence such as a letter sent by its head of clergy to a French bishop in 2001, commending him for not denouncing a paedophile priest who had been given 18 years jail for abusing young boys.
They are demanding a comprehensive Church policy for protecting the millions of children still in its care in schools, hospitals and youth groups worldwide, and the demotion of clergy who hid abuse in the past.
The Benedict papacy's response, O'Gorman said, "falls at the first and most important hurdle. That is to simply acknowledge the truth of what happened, and the truth of its role in the cover up of crimes by priests across the world."
With the victims still far from satisfied, the abuse crisis still hangs over the Vatican as the its cardinals - the "princes of the Church" - gather to elect Benedict's successor.
SIN OF A PRIEST
Cardinal Roger Mahony, who as archbishop of Los Angeles worked to shield paedophile priests from prosecution, according to files unsealed by court order in January, has expressed incomprehension about accusations levelled against the clergy over their handling of cases in the past.
"People say: 'Well, why didn't you call the police?' In those days no one reported these things to the police, usually at the request of families," he told the Catholic News Service on arrival in Rome.
The Vatican emphasised last week that it was the duty of cardinals to attend the conclave unless there was a serious impediment such as health. Britain's most senior cardinal Keith O'Brien excluded himself from the conclave after allegations he had behaved inappropriately with other priests.
He admitted his sexual conduct was not that expected of a priest. No allegations suggest this involved children.
Some cardinals have been suggested as "clean hands" candidates for the papacy, notably U.S. Cardinal Sean O'Malley, who was sent to Boston in 2003 to deal with an explosive abuse scandal that forced his predecessor, Cardinal Bernard Law, to step down and flee to a prestigious Church post in Rome.
Whoever the next pontiff is, he will face a scandal that caused two million Catholics to leave the Church in the United States alone, according to one University of Notre Dame study.
($1 = 0.7702 euros) (Editing by Philip Pullella and Michael Roddy)