Its advice to Dr Williams could determine whether the 77 million-strong Church stays together or shatters.

Saturday's decision by the Diocese of California to choose a married man rather than a homosexual as its next bishop avoided an immediate widening of the rift over gays.

To the relief of Dr Williams, the diocese belied its reputation for controversy by electing the Rt Rev Mark Andrus, even though two gay men and a lesbian were among the seven candidates. If California had picked a homosexual, it could have triggered even greater turmoil than that which followed the 2003 election by New Hampshire of the Rt Rev Gene Robinson, the first openly gay Anglican bishop.

But the General Convention, in Columbus, Ohio, will be an even more critical test of how far the liberal leadership in the US has pulled back from its radical agenda.

If the convention agrees to "repent" for its past behaviour, to avoid public blessings of gay "marriages" and to exercise extreme caution over gay bishops in future, Dr Williams hopes that the current fragile unity can be maintained.

But if it decides to push ahead with its liberal policies, he may have little choice but to refuse to invite its leaders to the 2008 Lambeth Conference, the 10-yearly gatherings of Anglican bishops.

Conservative Anglican leaders, mainly in Africa and Asia, have repeatedly called for the US Church to be expelled unless it repents for consecrating Bishop Robinson.

Dr Williams has used his diplomatic skills to rein back both extremes, but the convention's aftermath is expected to be his most testing period yet.

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