"I concluded that an active sexual relationship between two people of the same sex might therefore reflect the love of god in a way comparable to marriage, if and only if it had about it the same character of absolute covenanted faithfulness," said Archbishop of Canterbury Rowan Williams.
The controversial view, described by the top bishop as his "definitive conclusion" reached after 20 years of study and prayer, will infuriate the conservatives who boycotted the recent Lambeth Conference in the United Kingdom in protest at the presence of liberals who elected Anglicanism's first openly gay bishop.
Written eight years ago when Williams was the Archbishop of Wales, the private correspondence described his belief that Biblical passages criticising homosexual sex were not aimed at people who were gay by nature.
The contents of the letters, which were reported by The Times newspaper, were seen by the British daily.
At the Lambeth Conference, which closed on Sunday, the Archbishop recommitted the Anglican Communion to its orthodox position that homosexual practice is incompatible with scripture.
According to the London-based daily, the news threatens to reopen bitter divisions over ordaining gay priests, which pushed the Anglican Communion towards a split at the conference.
The controversial view of Archbishop Williams will also be perceived as an attack at conservative Anglican leaders who have since claimed that the Church is split following the consecration of Gene Robinson, the openly gay bishop of New Hampshire.
"It's no secret and no small matter that a significant part of the tension in the Anglican Communion is being played out in the heart of its leader," said Reverend Gregory Venables, a leading Anglican archbishop.
Many have accused the Archbishop of Canterbury of prolonging the crisis facing the communion. Senior Anglican bishops at the Lambeth Conference had called for a negotiated and an "orderly separation" in the communion to preserve the traditional identity of orthodox Christianity.