The Archbishop of Canterbury has warned that the worldwide Anglican Church faces a fundamental "rupture" on the issue of homosexuality.
Dr Rowan Williams told BBC One's The Heaven and Earth Show he feared any split could take decades to heal.
Traditionalists have given the Church in the US until June to reverse its approach on ordaining gay clergy - or face expulsion from the Communion.
Some liberals back a looser, federal structure for the Anglican Communion.
Dr Williams said he feared any split would run too deep to make this possible.
The archbishop, who is visiting Sudan, was speaking in an interview to be broadcast on Sunday.
"If there is a rupture, it's going to be a more visible rupture, it is not going to settle down quietly to being a federation," he said.
"And I suppose my anxiety about it is that if the communion is broken we may be left with even less than a federation."
'Starkest warning'
He warned that it could take decades to re-establish some sort of relationship between the different factions in the Anglican Communion.
BBC religious affairs correspondent Robert Pigott said the comments were "Dr Williams' starkest public warning about the impending schism in the Anglican Communion over sexuality".
Our correspondent said the archbishop seemed to be aiming his remarks at the American Church.
The church has been given until its governing convention meets in June to reverse its liberal approach to the ordination of gay clergy and the blessing of same-sex relationships.
Traditionalists insist that active homosexuality is outlawed by the Bible.
The ordination in the US of openly-gay Gene Robinson as a bishop has been threatening to split the communion.
Anomaly
His appointment as Bishop of New Hampshire in 2003 sparked a row across the Anglican Communion, with many conservative, evangelical and developing world priests outraged.
In a separate interview, Dr Williams criticised the US government's detention without trial of people at Guantanamo Bay.
He branded the detention camp in Cuba as an "extraordinary legal anomaly".
Dr Williams told Sir David Frost, in an interview for BBC News: "Any message given that any state can just over-ride some of the basic habeas corpus-type provisions, is going to be very welcome to tyrants elsewhere in the world, now and in the future.
"What, in 10 years' time, are people going to be able to say about a system that tolerates this."
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