BERLIN (Reuters) - Pope Benedict urged the faithful not to leave the Roman Catholic Church on Thursday as he began a four-day visit to Germany, where record numbers have quit the pews in protest against clerical sex abuse of youths.
The pope, on his third and toughest trip to his homeland, said on the flight from Rome he understood why some people -- especially victims and their loved ones -- were "scandalised by these crimes" and say "this is no longer my church".
But he asked them to see the Church comprised both good and bad, and was struggling to right the wrongs committed in its ranks. Germany has been rocked by the clerical sex scandals that have swept across Europe in the past two years.
"The Church is a net of the Lord that pulls in good fish and bad fish," he said, using the Gospel image of Jesus as a fisherman. "We have to learn to live with the scandals and work against the scandals from inside the great net of the Church."
A record 181,000 German Catholics officially quit the Church last year, for the first time higher than the number of Protestants leaving their churches and of baptisms into the Catholic Church.
The Church in Germany has received almost 600 requests for compensation for victims of sexual and physical abuse, while a victims' association estimates that more than 2,000 people were mistreated by Catholic priests in recent decades.
In the first of several protests expected during the day, four victims of sexual abuse gathered at the Brandenburg Gate around a large statue of a nun holding a stick to beat children with. On it was written the motto "Never Again!"
The pope told reporters on the plane that he was not concerned about the protests.
"It is part of our freedom and we must acknowledge that secularism and opposition to Catholicism in our societies is strong," he said. "But if opposition is expressed in a civil way then nothing can be said against it."
German President Christian Wulff -- a Catholic who has divorced and remarried in defiance of Church dogma on the sanctity of marriage -- and Chancellor Angela Merkel met the Bavarian-born pope at the airport.
In his welcoming speech at his official residence, Wulff hinted at his own situation by telling Benedict the Church now faced new challenges. "How mercifully does it deal with failures in people's private lives?" he asked.
He also asked about the Church's "failures in its own history and in the misconduct of its officials" -- a clear reference to the sex abuse scandals that have cast a shadow over many of the popes foreign voyages in recent years.
Benedict is expected to meet abuse victims at some point during this trip, as he has done in other countries, but no official announcement about this has been made.
Both Wulff and Benedict noted that religion's role was shrinking in Germany, where about one third of the population is Catholic, one third Protestant and one third unaffiliated or belonging to a minority faith like Judaism or Islam.
"You have come to a country where the Christian faith can no longer be taken for granted," he told the pontiff.
The pope then held talks with Merkel and was later due to address the Bundestag lower house of parliament, a session which about 100 left-wing deputies plan to boycott because they say it violates the separation of church and state.
An open-air Mass was planned at Berlin's Olympia Stadium in the early evening.
The pope's two previous visits home since his 2005 election were to the mostly Catholic regions of the Rhineland and his native Bavaria. This trip takes him to the mostly Protestant and atheist eastern part of Germany, where he can expect more criticism of his conservative policies.
On Friday, Benedict will travel to the eastern city of Erfurt to meet Protestant leaders in the monastery that once housed the 16th century reformer Martin Luther, whose teachings led to Europe's split between Catholics and Protestants.
Germany's Protestants hope he will allow joint communion services and let Protestant spouses of Catholics receive the Eucharist at Catholic Mass. The Vatican refuses these because it says Protestants understand the eucharist differently.
After Erfurt, Benedict will visit Etzelsbach where a small Catholic community withstood persecution under East Germany's officially atheist communist rule. He will end his German tour in the mostly Catholic southwestern city of Freiburg.
Writing by Tom Heneghan; Editing by Peter Graff and Elizabeth Piper