LONDON (Reuters) – The Archbishop of Canterbury, Rowan Williams, has urged the worldwide Anglican community to adopt an agreement designed to maintain unity over divisive issues such as gay bishops and same-sex unions.Williams, the spiritual leader of the world's 80 million Anglicans, is struggling to prevent disputes tearing apart the federation of 38 churches.

The proposed agreement, called a covenant, would require member churches to undertake not to act in a way likely to upset fellow Anglicans in other countries.

"It is an illusion to think that without some changes the Communion will carry on as usual," the Archbishop told the General Synod, the governing body of the Church of England, the Anglican mother church.

"The unpalatable fact is that certain decisions in any province affect all," he said.

"If we ignore this, we ignore what is already a real danger, the piece-by-piece dissolution of the Communion and the emergence of new structures in which relation to the Church of England and the See of Canterbury are likely not to figure significantly."

The covenant was first proposed in 2004 after tension rose over the consecration of an openly gay bishop at the Episcopal Church, the official US member church in the Communion.

Relations between Anglican churches became more fractious after conservative churches, mostly in Africa, responded by appointing bishops to serve in other countries, including the United States.

The covenant commits member churches to mutual accountability and consultation for settling disputes.

Unlike Roman Catholicism, Anglicanism gives its leader no direct power over all members.

The synod, newly elected for a five-year term, was due to discuss the covenant on Wednesday.

The covenant has polarised opinion among Anglicans, those on the liberal wing fearing it could result in a dogmatic, centralised disciplinary structure.

Conservative Anglicans support the covenant, but have complained it no longer goes far enough in disciplining churches which step out of line.

Liberal groups launched an international campaign against the covenant last month, saying it threatened to reinstate control by foreign bishops, something King Henry VIII rejected nearly 500 years ago when he broke away from the Roman Catholic Church based in Rome.

The Anglican Church of Mexico is the only province to have accepted the covenant so far.

Williams said the pact would not create a centralised system, and that it was "dispiriting to see the Covenant still being represented as a tool of exclusion and tyranny".

Another divisive issue the Church of England (CoE) is set to discuss during the current parliamentary term is the consecration of women as bishops.

The Queen, supreme governor of the CoE, said during the synod's formal opening that the next five years "will not always be straightforward", and many issues had yet to be resolved.

"Some will, no doubt, involve difficult, even painful, choices," she said.

"But Christian history suggests that times of growth and spiritual vigour have often coincided with periods of challenge and testing."