LONDON (Reuters) - Archbishop of Canterbury Rowan Williams, who has agonised about schisms in the Anglican Communion over women and gay bishops and same-sex unions, announced unexpectedly on Friday that he would step down at the end of the year.
He said it was time to move on after a decade as archbishop and his new post as master of Magdelene College at Cambridge University would give him the time "which I have longed for" to think and write about the Church.
"I would hope that my successor has the constitution of an ox and the skin of a rhinoceros," he said.
Williams, 61, a white-bearded and bushy-browed theologian, will leave behind a church split between progressives ready to allow women bishops and bless same-sex unions, and conservatives opposed to such modern reforms.
His resignation also appeared to spell the end for his faltering project to forge more unity in the Anglican Communion, an 80-million strong worldwide federation of 38 national and regional churches that see him as their spiritual leader.
He acknowledged these strains in an interview with Britain's Press Association, saying that crisis management was "never a favourite activity" and had actually been "major nuisance" during his tenure.
"There are some conflicts that won't go away, however long you struggle with them," he said. "Not everybody in the Anglican Communion or even in the Church of England is eager to avoid schism or separation."
Frontrunner to replace him is the Church of England's second highest cleric, Archbishop of York John Sentamu. Born in Uganda, he fled to Britain in 1974 to escape from dictator Idi Amin.
Sentamu praised Williams as "God's apostle for our time", a courageous and holy man who had been "much maligned by people who should have known better".
Elizabeth Hunter, director of the London-based religious think tank Theos, described Sentamu as more conservative than Williams. But she did not see him making a sharp break in the Church or the Communion.
"Anyone who gets this post will not take a radical diversion from the path that Archbishop Rowan has been treading simply because there really isn't any other choice.
"They'll just continue with these slightly awkward compromises and uncomfortable conversations, where you sometimes get to wondering really is it one church at all, or two or three," she said.
Unlike the centralised Roman Catholicism, Anglicanism is a loose family of member churches with the Archbishop of Canterbury as its spiritual leader. As such, Williams had prestige and respect, but no direct powers beyond the Church of England he leads.
A Welshman, Williams taught at Cambridge and Oxford universities before becoming a bishop and won international respect as a modern Christian theologian. He stood out for his liberal views, protesting against nuclear weapons and advocating a more accepting Anglican approach towards homosexuality.
After becoming archbishop in 2002, he moved to more centrist views and made several concessions to conservatives in the Church of England and in the Anglican Communion to try to keep them from splitting away.
In the process, however, he ended up disappointing both progressives and traditionalists and lost some of his authority.
"His efforts have run into the sand," said Clifford Longley, a commentator on religious affairs. "He's not managed to do what he hoped he would be able to do."
In July, the Church of England's General Synod, or parliament, looks likely to allow women priests to become bishops, with the same status as men, after rejecting Williams's proposal of a reduced status for the women to satisfy traditionalists who struggle with the idea of female clergy.
The compromise was a bid to keep traditionalist Anglo-Catholics from taking up an offer from Pope Benedict to switch to Rome within an ordinariate created just for them. About 50 traditionalist priests have left and more are due to follow.
The ordinariate, which the Vatican informed him of only shortly before announcing it, was seen as another setback to his authority. But his personal ties to the pope were warm and he prayed with him in Rome just last week.
Not all conservatives plan to lead. Rev. Rod Thomas, head of the Reform network of evangelicals within the Church, signalled his group would keep up pressure against reforms by saying the next archbishop needed "to hold firm to Biblical truth in areas such as human sexuality."
The Synod also looks set to reject the Anglican Covenant, Williams' plan to heal a rift created between western and African churches when a Canadian Anglican diocese approved blessings for same-sex couples in 2002 and the Episcopal Church, U.S. Anglicans, appointed an openly gay man as bishop in 2003.
Led by Archbishop Peter Akinola, the then head of the Church of Nigeria, Anglican churches in Africa, Asia and Latin America denounced these innovations as un-Biblical and built a network that threatened to break away from the Communion.
Several U.S. and Canadian parishes and dioceses switched their alliegence from their liberal national churches to conservative African churches. Others formed their own Anglican Church of North America, which claims over 100,000 members.
Williams, who worked tirelessly to keep the churches together, championed a plan to give the Communion the authority to tell member churches when they overstepped doctrinal boundaries and shut them out of some international Anglican committees if they did not pull back.
The plan originally called for stiffer sanctions against churches that did not heed the Communion's call to stay in line with the other members. But this faded in successive versions of the Covenant, disappointing conservative churches who originally backed it as a way to discipline liberal churches.
Only a few national churches have now approved the final proposal and the Church of England, where many members think it centralises Anglicanism too much, looks set to reject it because a majority of dioceses voting on it so far have said "no".
That would scuttle the project, said Jim Naughton, editor of the U.S. church news website Episcopal Cafe. "What kind of Anglican Communion is it if the Archbishop of Canterbury's church isn't part of it?" he asked.
Differences over issues of human sexuality persisted, he said, but the spectre of schism has faded in recent years.
"A lot of the firebrand leaders in Africa have retired and their successors are not as interested in going toe to toe," he said. "As a result, the furor is dying down."
Apart from Sentamu, Bishop of London Richard Chartres is also in the running to succeed Williams. Closer to the Anglo-Catholic wing of the Church, he is seen as a serious thinker who speaks more clearly than Williams's sometimes dense style.
But his chances may have suffered over St Paul's Cathedral's botched handling of a four-month-long anti-capitalist movement Occupy London camp on its doorstep.
Hunter said Sentamu was "a talented communicator" who would bring a new style to the Church and the Communion.
"His heritage and his background and his sensitivity towards the churches in the developing world would probably be a very helpful thing at this time in the Communion," she said.
"There's a lot of people within the church who think there's a freshness to him after a sort of scholarly dustiness that has been sprinkled over some of Archbishop Rowan's announcements."
Longley said the role of spiritual leader of the worldwide Anglican Communion "is verging on the impossible" and member churches could run out of patience with the British monopoly on naming the archbishop.
"The Anglican Communion probably ought to be a looser federation," he said. "It's not really the end of the world."
Katharine Jefferts Schori, presiding bishop of the Episcopal Church, thanked Williams for his service "during an exceedingly challenging season." During Williams's tenure, the Episcopal Church ordained two gay bishops, Gene Robinson in 2003 and Mary Douglas Glasspool in 2010.
"We can all give thanks for his erudition and persistence in seeking reconciliation across a rapidly changing Anglican Communion," she said in a statement.
Additional reporting by Tom Heneghan in Paris and Andrew Stern in Chicago.; Editing by Angus Macswan