CANTERBURY, England — The head of the Anglican Communion said yesterday that the global fellowship faces “one of the most severe challenges” in its history, and he urged bishops at their once-a-decade Lambeth Conference to do the hard work of finding solutions.

Archbishop of Canterbury Rowan Williams said the Anglican family’s most immediate need is for “transformed relationships” so they don’t break apart over homosexuality and the Bible.

“We all know that we stand in the middle of one of the most severe challenges to have faced the Anglican family in its history,” he said in an address to the 650 bishops at the assembly.

But he said the world fellowship has survived other crises in its centuries-long history, and he has faith that church leaders can overcome the most recent troubles.

“Whatever the popular perception, the options before us are not irreparable schism or forced assimilation,” Archbishop Williams said. “It is not an option to hope that we can somehow just carry on as we always have.”

Archbishop Williams made the comments as church leaders in Canterbury emerged from days of prayer and turned to the business of their meeting. In Bible study and small group discussion, they will try to rebuild the ties among Anglican national churches that shattered after the 2003 consecration of the first openly gay Episcopal bishop, V. Gene Robinson of New Hampshire.

The work of the meeting, which runs through August 3, is complicated by a boycott. About one-quarter of the invited bishops — theological conservatives mostly from Africa — stayed away because Archbishop Williams invited bishops from America and elsewhere who accept gay relationships.