For many evangelical Christians in the US, opposition to the physical expression of homosexuality is quite literally an article of faith. It is part of their definition of orthodoxy. "Gay Christian" is almost a contradiction in terms: you can be homosexually oriented, but if you are, you are expected to be celibate. For most, the move in liberal and mainstream denominations towards accepting gay marriage as permissible and normal is horrifying. Far from representing the open and welcoming stance typical of Jesus himself, it's apostasy. Homosexuality is a psychological disorder at best, a perversion at worst.

However, Western culture in general is moving inexorably towards greater acceptance. After a bitterly-fought battle, the US Supreme Court declared same-sex marriage legal there. Other countries, including the UK, were already there.

Now a report from the respected Pew Research polling organisation has indicated what observers had suspected: that the Churches were not immune to changing attitudes in wider culture.

The report shows more than a third of evangelical Protestants now believe that homosexuality should be accepted by American society, up 10 points from 2007. The change is being driven partly by young adults, who are more accepting than older people – 51 per cent of Millenials say that homosexuality should be accepted, compared with only a third of Baby Boomers – but, the report says: "While it is true that young adults are more accepting of homosexuality than are older adults, it is also true that older adults have become more accepting of homosexuality over time."

It's important to be clear exactly what this means, and surveys are not always good at this. For example, it's possible to believe that same-sex marriage is wrong and that Christians should never enter into one, and still believe that it should be legal. However, it does seem that over the issue of homosexuality, Christian attitudes are being shaped by the wider culture. So how are evangelical churches responding? I see three distinct responses:

1. Churches that hold the line. These churches continue to preach and teach that homosexual behaviour is sinful and that they can't compromise on what the Bible says.

At one level this is fine: evangelical churches have a strong sexual conduct ethic and this is another expression of it. The difference is that while marriage is usually a theoretical option for single heterosexuals, on this view it isn't for single homosexuals. So these churches will have to decide how they want to treat gay members of their congregations who do enter into physical relationships – as a single heterosexual person might – and whether they will see homosexual sin as worse than heterosexual. They also need to be willing to acknowledge that their appeal to the gay community will be limited, and that their own congregation will continue to be affected by the currents of change. They may not be gay, but they will have friends, neighbours and family who are.

2. Churches that 'give' a little. Some churches draw a distinction between 'welcoming' and 'affirming' gay people. In the former, they are welcome to participate as fully as possible in the life of the church – including taking communion – with the reservation that the church doesn't accept that it's right for them to express their homosexuality in a physical relationship. The emphasis is on God's grace and on the personal relationship between him and the person concerned. The rightness or otherwise of particular actions are left to their own consciences.

One problem with this approach is that the difference between welcoming and affirming becomes a distinction without a difference. Those who want to maintain the fundamental wrongness of homosexual behaviour are subverted by its normalisation in the process of welcoming and integrating gay people.

A second problem is that it doesn't feel very welcoming to gay people. A church might feel that it's gone a long way if it refuses to condemn a same-sex relationship and invites gay people to the Lord's table on equal terms with straight people, but it's still making a mental reservation. While it's an attractive idea for those who want to be theologically orthodox but pastorally sensitive, it isn't necessarily going to work.

3. Churches that accept the fait accompli. Denominations like the Episcopal Church allow clergy to perform same-sex marriages. Many from traditional denominations have come to believe that same-sex relationship should be treated as the moral equivalent of opposite-sex.

While this view allows these Churches to continue to have a pastoral relationship with the gay community largely denied to conservative evangelicals, the latter argue that it flies in the face of the plain sense of scripture.

Evangelicals in the US – and in the UK – face an immensely difficult few years. Churches that continue to preach a hard-line rejection of homosexual and transgender people will become increasingly detached from wider culture. It's likely that the small number of legal victories they will win against anti-discrimination legislation – like Houston's HERO ordinance – will create a strong sense of group identity at the same time as alienating more and more people. Given the size of the evangelical subculture it will take a good while for this to impact seriously on numbers, but it will. Influence and credibility will have suffered before then.

On the other hand, churches that seek to take a middle way – welcoming but not affirming – will also suffer. They will inevitably be pulled to one extreme or the other, with the likelihood that they will become affirming in practice if not in principle.

Churches that do both welcome and affirm gay people – conducting their weddings and calling them to ministry – will have their problems too. They might like to think of themselves as evangelical, but they will have largely put themselves beyond the evangelical pale. Furthermore, their rejection of traditional teaching about homosexuality also has implications for their view of the inspiration of Scripture – a very awkward theological problem. These churches may find themselves evangelical in culture and language, but without the rigorous theological underpinnings which used to support them.

There are no easy ways forward for evangelicals on this. But even the most convinced opponent of homosexual behaviour must find a way of speaking, and being, good news. No one must be excluded from the call and promise of the Gospel.

Follow @RevMarkWoods on Twitter.