The Catholic Church has a vital role to play in shaping social policies but does not seek to usurp secular authorities, Pope Benedict said on Saturday.

In a homily to pilgrims in southern Italy, the Pope said the Church's role in politics - where it often speaks out against abortion, gay marriage and embryo research - was not intended to take the place of western secular ways of government.

"The Christian community cannot and does not want ever to substitute the legitimate and right competencies of institutions," the Pope told pilgrims at the start of a two-day visit to one of Italy's most economically depressed areas.

He spoke at an open-air mass on a cliff 100 metres (330 feet) above the Mediterranean Sea at one of the southernmost points of the Italian mainland.

A day after strolling through the Vatican Gardens with US President George W Bush, with whom he sees eye-to-eye on many moral issues, the Pope said the Church had the role of "supporting (governments) in their work and always proposes cooperating with them for the good of all".

The Church often comes under fire from left-wing politicians in Italy, Spain and some other predominantly Catholic countries who accuse it of interfering in domestic affairs.

After the April election of a new conservative government, former foreign minister Massimo D'Alema warned the Church against succumbing to "the demoniacal temptation of seeking power" by forging a pact with new prime minister Silvio Berlusconi.

Pope Benedict, wearing gold and cream vestments as he celebrated the mass, said the Church's role in influencing policy-making was especially important in societies where individualism, rather than the common good, is championed.

"Good wins out," he said in his homily.

"And, if at times it can seem to be defeated by bullying and cunning, in reality it continues to operate in silence and discretion, bearing fruit in the long term," he told the crowd of some 5,000 people who packed a small square.

Berlusconi himself has said his government is in favour of the Church. "The activity of the government can only please the Pope and his Church," he said earlier this month.

But Berlusconi's policies have not always coincided with the Vatican's views.

The Church has expressed concerns about a current government crackdown on immigration and Pope Benedict's predecessor John Paul II was against the 2003 US-led invasion of Iraq, which was supported by Berlusconi.

Among the local dignitaries to welcome the Pope to the seaside town of Santa Maria di Leuca was Nichi Vendola, an openly gay communist who is governor of Puglia, the "heel" of Italy.