CANTERBURY, England — The world's Anglican bishops turned Saturday to the enormous task at the heart of their once-a-decade summit: trying to keep the Anglican family from breaking apart over the Bible and homosexuality.

With its private prayer phase over, the business of the Lambeth Conference begins, but it is hobbled by a boycott: about one-quarter of the invited bishops — mostly theological conservatives from Africa — are not attending.

The 650 bishops who are here include a mix of traditionalists, moderates and liberals, all with divergent ideas about what Anglicans should believe and how their fellowship should operate.

The conference's opening public worship is set for today in Canterbury Cathedral. Archbishop of Canterbury Rowan Williams, the Anglican spiritual leader, has led a three-day closed-door session this week focused on the role of the bishops as seen through the Gospel.

Archbishop Williams designed the entire gathering without any votes or resolutions. Instead, the bishops will hold daily Bible study and small group discussions. They plan to release their collective "reflections" on the meeting when it ends Aug. 3.

The 77 million-member Anglican Communion has been splintering since 2003, when the Episcopal Church, the U.S. Anglican body, consecrated the first openly gay bishop, V. Gene Robinson of New Hampshire.

Bishop Robinson's election has also complicated Anglican relations with other Christians.

The Vatican's No. 2 official, Cardinal Tarcisio Bertone, said in a letter of greeting to the conference that was released Saturday night that, "New issues that have arisen in our relationship pose a further and grave challenge to the hope for full and visible unity that has been the long-standing goal" of their efforts to rebuild ties.

Anglicans split from Rome more than four centuries ago when English King Henry VIII bolted in 1534 after he was refused a marriage annulment. The Vatican has spoken against the Church of England's recent move to appoint women bishops.

Last month, Anglican conservatives — frustrated that Archbishop Williams hasn't done more to keep the U.S. church and other liberal Anglicans in line with traditional Bible teaching — formed a new global church network that circumvents the archbishop's authority but stops short of schism.

A few leaders of that movement are attending Lambeth, but most have stayed away. They released a statement ahead of today's service condemning "false teaching which justifies sin in the name of Christianity."

"These are not merely matters of different perspectives and emphases," they wrote. "They have led to unbiblical practice in faith and morals, resulting in impaired and broken communion. We long for all orthodox Anglicans to join in resisting this development."

Some critics have said the program is an attempt to avoid decisive action.

Archbishop Phillip Aspinall, head of the Anglican Church of Australia, defended the conference design Saturday as "not backing away from the hard realities we have to face, but nurturing the right spirit" to confront them.

Archbishop Williams has told bishops they must "call everyone together" instead of aligning with one group or another. He also said bishops must not only listen to the people they lead, but also consider what God wants of them, according to bishops who discussed details of the private talks.

In one session, Archbishop Williams asked the bishops, seated in the nave of the historic cathedral, to go pray with another bishop who they feel nervous about meeting, according to U.S. Episcopal Bishop George Councell of New Jersey.

Several bishops said as they looked around the cathedral, they were struck by the tombstones of Anglican church leaders who had served hundreds of years ago.

It was a reminder not only of the history of the Anglican fellowship but also of its ability to survive turmoil, Councell said.

"We've been at this a long time," he said.

The Anglican Communion is a global fellowship of churches that trace their roots to the missionary work of the Church of England. It is the third-largest group of churches in the world, behind Roman Catholics and Orthodox Christians.

The communion has long held together different views of ritual and Scripture. But its biggest and fastest-growing churches are now in Africa and other developing regions where strict interpretation of the Bible is the norm.

The wealthy but much smaller liberal-leaning churches in the U.S., Canada and Western Europe have seen dramatic drops in membership.

Williams barred Robinson and a few other problematic bishops from the Lambeth Conference to ensure broader participation. But he invited U.S. leaders who consecrated Robinson and bishops from other Anglican provinces that accept gay relationships.

Robinson has traveled to Canterbury anyway, hoping to meet with as many overseas Anglican bishops as possible. Advocates for gay and lesbian Anglicans have also set up in Canterbury, planning an opening service of their own in another church today.