(CNN) -- Pope Benedict XVI is expected to meet the Archbishop of Canterbury on Saturday, the first meeting between the religious leaders since a Catholic overture to disaffected Anglicans that some commentators compared to a hostile takeover on Wall Street.



Rowan Williams, the nominal head of the world Anglican Communion, threw down a theological gauntlet to the pope in a highly challenging speech in Rome in the run-up to their meeting.



He laid out a series of questions suggesting that decades of hard-won apparent reconciliation between the Catholic Church and other Christian denominations might have weak foundations.



He also proposed that a truly universal Christian church might have to be structured more like the Anglican Communion -- with no central authority laying down the law -- than like the Catholic Church, with the pope on his throne.



"Is there a mechanism in the church that has the clear right to determine for all where the limits of Christian identity might be found?" Williams asked. "Is the integrity of the church ultimately dependent on a single identifiable ministry of unity to which all local ministries are accountable?"



The meeting comes in the wake of a Vatican move that some say will shatter more than 40 years of efforts to reconcile the Catholic and Anglican churches.



The Vatican announced in October that it had worked out a way for Anglicans who are dissatisfied with their church to switch allegiance en masse to Rome.



The process will enable groups of Anglicans to become Catholic and recognize the pope as their leader, yet have parishes that retain Anglican rites, Vatican officials said. The move comes some 450 years after King Henry VIII broke from Rome and created the Church of England, forerunner of the Anglican Communion.



The number of Anglicans wishing to join the Catholic Church has increased in recent years as the Anglican Church has welcomed the ordination of women and openly gay clergy, said Cardinal William Joseph Levada, the head of the Vatican's Congregation for the Doctrine of the Faith, in announcing the move in October.



Williams was said to have been taken by surprise by the move, which critics described as an end run around a long-established Catholic-Anglican dialogue.



"The Catholic Church is responding to the many requests that have been submitted to the Holy See from groups of Anglican clergy and faithful in different parts of the world who wish to enter into full visible communion," Levada said.



Levada said "hundreds" of Anglicans around the world have expressed their desire to join the Catholic Church. Among them are 50 Anglican bishops, said Archbishop Joseph Augustine Di Noia of the Congregation for Divine Worship.



Catholic and Anglican theology and rites are broadly similar, but Anglicans have long allowed priests to marry and have children.



In recent decades, the Anglican Communion has allowed women to become priests. The Episcopal Church, the United States branch of the Anglican Communion, has ordained an openly gay bishop, Gene Robinson, and appears to be on the verge of ordaining more.



Those developments have caused controversy within the communion, with more conservative parishes setting up alternative structures of authority.



Pope Benedict hinted clearly when he last met Williams in Rome almost exactly three years ago to the day that Rome did not look kindly on the Anglican moves.



"Recent developments, especially concerning the ordained ministry and certain moral teachings, have affected not only internal relations within the Anglican Communion but also relations between the Anglican Communion and the Catholic Church," the pope said in November 2006.



"We believe that these matters, which are presently under discussion within the Anglican Communion, are of vital importance to the preaching of the gospel in its integrity, and that your current discussions will shape the future of our relations," he added.



There are about 77 million Anglicans worldwide, and about 1.1 billion Roman Catholics.
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