Increasing numbers of young adults in the United States do not consider themselves to be Christian.

Many do not take a biblical world view on key social and moral issues. And large numbers support developments such as same-sex marriage. 

The survey of younger adults in the US for the Worldview Measurement Project and carried out by the American Culture and Faith Institute shows that millennials are by far the generation least likely to possess a 'biblical worldview'.

Millennials also represent 'one of the most spiritually challenging generations to reach adulthood in the past century', says the institute: 'While the Baby Boom generation broke the mould of faith traditions and preferences some 50 years ago, Millennials are raising a new set of challenges to Christianity and to a nation whose morals and values have long reflected biblical principles.' 

Millennials, America's largest generational cohort, are defined as those born in the last two decade of the 20th century.

George Barna, executive director of the institute, said younger adults have historically held less conservative values than their elders.

'The question that remains is how much the views of Millennials will eventually move to the right on the ideological continuum.

'The challenge to conservatives is that the current views of Millennials are so far to the left-of-centre that even a typical amount of repositioning over time will leave the youngest generation considerably more liberal than desired, and more distant from traditional norms than has been the case during our lifetime.'

He said a person's worldview is typically developed between the ages of about 18 months and 13 years.

'There is usually very little movement in a worldview after that point. You could say with confidence that the worldview a person possesses at age 13 is probably the worldview they will die with. Unless pre-existing patterns radically change, we are not likely to ever see the Millennial generation reach even 10 per cent who have a biblical worldview.'

Parents are one of the most important influences on what children believe.

But because 24 of every 25 Millennials lack a biblical worldview today, the probability of them transmitting such to their children is extremely low.

'You cannot give what you don't have, said Barna. 'In other words, if today's children are going to eventually embrace a biblical worldview, people with such a perspective must exert substantial influence on the nation's children to supply what their parents are unable to give them.

'The United States goes to great lengths to assist in the economic welfare of millions of people. It appears that we now need those who possess a biblical worldview to step in and impact the spiritual well-being of our future adults as well.' 

The survey found that just 59 per cent of Millennials consider themselves to be Christian, compared to 72 per cent of adults from older generations. Nearly three out of every 10 Millennials claims to be atheist, agnostic or 'none'.

And while one in three older adults is born again, believing they will experience eternity in Heaven with God after their death on earth because they have confessed their sins and accepted Jesus Christ as their saviour, just one in five millennials share this belief.

While minority of adults 30 or older – 43 per cent – supports same-sex marriage, nearly two-thirds of those under 30 – 65 per cent – support it.