The world's first openly gay Anglican bishop described the decision to bar him from a landmark Church leaders' conference as a "mistake".
The Rt Rev Gene Robinson said he sympathised with Archbishop of Canterbury's position, but added that the lack of an invite meant the Lambeth Conference would not benefit from the inclusion of a gay voice.
Due to commence on Tuesday, the once-in-a-decade meeting of Anglican bishops comes as the Church continues to disintegrate over the issue of homosexuality and women priests.
Despite the snub, Mr Robinson - whose ordination as Bishop of New Hampshire in 2003 split the Anglican Communion - will be in Canterbury at the time of the conference.
Speaking on BBC's The Andrew Marr Show, Mr Robinson said: "I think a mistake was made in not including me in those conversations. I was the only openly gay voice that might have been at the table. But I will do all I can from the fringe."
But he added that he did sympathise with Dr Rowan Williams' position.
He said: "He is in an almost untenable position. No matter what he does he will make someone mad and sometimes everybody mad.
"There is no doubt in my mind that his aim is to hold our beloved church together."
The bishop will deliver a sermon in the UK as the Church continues to be divided over the issue of homosexuality.
It comes at a particularly sensitive time for the Church. Earlier this month conservatives set up a splinter movement in rejection of the acceptance of gay bishops. And last week the General Synod descended into acrimony after the Church of England's ruling body voted in favour of legislation aimed at introducing women bishops.
