The controversial document, produced by the Congregation for Catholic Education and Seminaries, the body overseeing the church's training of the priesthood, is being scrutinised by Benedict XVI.

It been suggested Rome would publish the instruction earlier this month, but it dropped the plan out of concern that such a move might tarnish his visit to his home city of Cologne last week.

The document expresses the church's belief that gay men should no longer be allowed to enter seminaries to study for the priesthood. Currently, as all priests take a vow of celibacy, their sexual orientation has not been considered a pressing concern.

Vatican-watchers believe the Pope harbours doubts about whether the church should publish the document, which has already been the subject of three drafts.

'Inevitably, such a directive will be met with opposition,' said John Haldane, professor of moral philosophy at the University of St Andrews.

The instruction tries to dampen down the controversy by eschewing a moral line, arguing instead that the presence of homosexuals in seminaries is 'unfair' to both gay and heterosexual priests by subjecting the former to temptation.

'It will be written in a very pastoral mode,' Haldane said. 'It will not be an attack on the gay lifestyle. It will not say "homosexuality is immoral". But it will suggest that admitting gay men into the priesthood places a burden both on those who are homosexual and those they are working alongside who are not.'

The instruction was drawn up as part of the Vatican's response to the sexual abuse scandal that surfaced in the American church three years ago, which has seen hundreds of priests launch lawsuits against superiors whom they accuse of abusing them.

As the former head of the Congregation of the Doctrine of the Faith, the Vatican body charged with looking into the abuse claims, Benedict, then Cardinal Joseph Ratzinger, was made acutely aware of the scale of the problem. He is thought to have made clearing up the scandal one of the key goals of his papacy.

Next month the Vatican will send investigators to the US to gauge the scale of the scandal. More than 100 bishops and seminary staff will visit 220 campuses. They will review documents provided by the schools and seminaries and may interview teachers, students and alumni, then report directly to the Vatican, which could choose to issue the instruction barring homosexuals from entering the priesthood as part of its response.

Studies show that a significant proportion of men who enter seminaries to train for the priesthood are gay. Any move signalling that homosexuals will not be allowed to join the seminaries, even one couched in the arcane language of the Vatican, could reduce the number of recruits to the priesthood.

In a further sign of the instruction's deeply controversial nature, it is expected the document would be signed by a cardinal rather than the Pope himself if the Vatican decides to publish it.

The Vatican has been carefully trying to soften Benedict's image since he was elected earlier this year. In recent weeks he has reached out to the Jewish and Muslim communities as well as young Catholics during the church's World Youth Day. The initiatives have been seen as a significant PR success. A decision to publish an instruction that would underscore his religious conservatism would be detrimental to Benedict's standing as he enjoys his 'honeymoon period' on the world stage.