The religion is also waning in popularity with a rapid increase in people describing themselves as 'non-Christian' since the same poll was conducted in 1996.
91% of young non-Christians and 80% of young churchgoers said "anti-homosexual" describes Christianity.
Further research found that both groups said that Christians "show excessive contempt and unloving attitudes towards gays and lesbians."
Young Christians told researchers that the church has made homosexuality a "bigger sin" than anything else and not helped them apply the biblical teaching on homosexuality to their friendships with gays and lesbians.
Overall, the Barna found that the younger generation is much more sceptical and critical of Christianity today, whether they are or are not believers.
Christianity's 'image problem', as Time magazine describes it, is in need of a major overhaul.
The Barna research was highlighted in a comment piece on Christian website Ekklesia.co.uk by commentator Tim Nafziger, who said it raised profound questions for churches.
"A whopping 80% of non-Christians surveyed had spent at least six months attending church," he wrote.
"These are not casual cynics, jaded by the media. They are people who have tried Christianity and found it wanting. In other words, all of us Christians are responsible.
"We can't just point our fingers at some other part of the church or secular society. Where have we failed to model the radical hospitality of Jesus?"
Christians are 'anti-homosexual' according to US poll (PinkNews 4.10.07)
Homophobia turns young people off Christianity (PinkNews 18.10.07)