The moderator of the Church of Scotland has revealed that she is “terrified” of an upcoming debate on the ordination of gay ministers, which has the potential to cause the largest schism within the church since the 19th century.

The Church of Scotland is due to decide whether it will continue to allow the ordination of lesbian and gay ministers on the condition that they remain celibate. A lot rests on the decision, which will take place following a debate on Monday 20 May.

50 congregations have intimated that they may leave the church over the issue. Although they may only be a small part of over 1,400 congregations that make up the church, it would still mark the largest split since the Disruption of 1843.

Reverend Lorna Hood, Moderator of the Church of Scotland’s General Assembly, will be chairing the debate.

She told the Sunday Times: “I’m terrified. Fear and excitement vie for first place in my mind all the time. But the amount of support — cards, letters and congregations offering to pray for me — has been absolutely overwhelming. I have to rest on that and be carried by that. So I just think: come on, get on with it.”

She compared the issue to the decision to ordain women as ministers, which she claimed was even more divisive.

“The ordination of women was for a number of presbyteries a huge, huge issue but here we are now,” she said. Reverend Hood added that she hoped the use of professional mediators during the debate would help prevent a split.

Reverend Bruce Dempsey, the head of two congregations in Coupar Angus, said he was dismissive of her hopes of compromise: “I am not sure what room for mediation there would be. If we are talking about a complete departure from what the Bible teaches, then it follows that the Bible is no longer considered the Church of Scotland’s supreme rule for faith and life.

“The question then is, what is? Where does that leave the integrity of all of the church’s teachings?”

He added: “We cannot cherry pick the Bible to suit ourselves. To my mind the Bible is unambiguous and very clear. In this case it is an either/or situation. There is no middle ground.”

A poll by the Theological Commission On Same-Sex Relationships And The Ministry found that 57.8% of individual presbytery members were against individuals in same-sex relationships being ordained, while 35.4% were in favour.

In February, the Rev Dominic Smart and his congregation of 300 at Gilcomston South in Aberdeen left the Church of Scotland over the ordination of gay ministers.

The congregation took issue with the General Assembly approving the appointment of the openly gay minister Scott Rennie to Queen’s Cross church in Aberdeen in 2009. St George’s Tron in Glasgow has also elected to leave the kirk over the issue.