More than four out of 10 evangelical pastors are still undecided about who to vote for in the US election, in spite of efforts by Donald Trump's running mate Mike Pence to reassure Christian voters.

According to a new report from Nashville-based LifeWay Research, nearly a third of pastors plan to vote for Donald Trump while fewer than one fifth will vote for Hillary Clinton.

Four per cent support Gary Johnson and three per cent do not plan to vote. Just one in 100 has endorsed a candidate from the pulpit.

Lifeway surveyed 1,000 senior pastors between August 22 and Septemper 16.

Executive director Scott McConnell said: "Donald Trump does better with pastors than Hillary Clinton. But both candidates are still less popular than 'undecided'."

More than a quarter said personal character matters most and a fifth are most concerned about a candidate's probable Supreme Court nominees. African-American pastors are most likely to vote for Clinton while white pastors favour Trump.

According to the Baptist Press report of the vice-presidential debate, when discussion turned to religion and social issues, both candidates professed "deep personal faith" but applied it to public policy in contrasting ways.

Another new survey, from Barna, found most Americans are not happy with the status quo. In particular, nine out of 10 conservatives believe the US is heading in the wrong direction. Just 14 per cent of evangelical Christians feel "well-served" by the federal government.  Barna found that overall, 31 per cent of evangelicals had a favourable disposition toward Trump while just 17 per cent had a similar perception of Clinton.