"My visit this autumn is an opportunity to continue that rich tradition of visits between Canterbury and Rome," said Williams, struggling to avoid schism in his own church over the ordination in America of openly gay bishop Gene Robinson.

The blessing of same-sex unions in Canada's Anglican Church and moves to ordinate women bishops in the Church of England are two other issues that could drive Protestants and Catholics further apart.

"We are living in an ecumenical winter," admitted former Archbishop of Canterbury George Carey who visited Pope John Paul six times.

"It has got even icier since the American church's decision to consecrate Gene Robinson which goes completely against the Catholic position and the historic position of the Anglican communion as well," he told the Times.

Carey hoped the personal chemistry between Williams and Pope Benedict would help to mend bridges.

The Roman Catholic Church, which accounts for just over half of the world's 2 billion Christians, has been working since the Second Vatican Council (1962-1965) with its "separated brothers" to try to overcome the splits in Christianity.

While the differences are too great to draw everyone in under one roof, Benedict advocates "unity in diversity" that could bring Christian churches closer together.

But the contrast between the way the two Churches are run remains an ecumenical headache for both leaders.

Headquartered in the Vatican, the Catholic Church is run like a monarchy led by a powerful Pope atop a descending pyramid of cardinals, archbishops and bishops around the world.

Anglicanism, which dates to Henry's break with Rome, built up a much looser structure of 38 churches around the world. It now has 77 million members.

Williams, "first among equals" with moral authority but no legal power, has bemoaned the way the gay bishops row is tearing his church apart and acknowledged this week there might come a moment when the Anglican Communion says "We can't continue like this."

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