An audience of Christians has given conservative West Australian Premier Colin Barnett rousing applause at an election debate but opposition leader Mark McGowan got the most laughs despite the weighty topics.

Speaking at an Australians Christian Lobby forum on Tuesday night, Mr Barnett said he would push ahead with plans to regulate the prostitution trade, possibly adopting a Swedish law, whereby it is illegal to procure sexual services.

"That was considered at length in our party room and debated at length. We decided not to go down that path," he said. "We took the line that ultimately legislation would be introduced, explored in parliament, so if we're re-elected, we'll have to go back and revisit that and I'm sure the argument and debate about the Swedish model and others will take place."

Mr Barnett said the most important act of his government had been to stop small brothels springing up in the suburbs.

It had also introduced legislation to contain prostitution to limited areas such as entertainment districts, he said.

But Mr McGowan said that proposal - to legalise prostitution in certain areas - was one he didn't back.

"We're not going to support their law," he said. "Within the laws that the government has proposed is a requirement, if you like, for anyone who might work in prostitution to be registered as someone on a government database.

"I don't want to put people through that particular requirement."

Mr McGowan reiterated his support for gay marriage, saying it was a federal issue, but if he was a member of federal parliament, he'd vote for it.

Mr Barnett drew applause from the crowd when he said he did not support it, and that marriage was meant to be between a man and a woman.

On the question of whether children conceived from a surrogate arrangement should be able to access information about their biological parents, the Premier said he was "not all that comfortable" with surrogacy, although he recognised that some couples could not have a child.

Mr Barnett said he would rather see more adoption, and it should be easier to do so.

Mr McGowan said he believed current laws that required someone wanting to adopt to be no more than 45 years older than the child were discriminatory.

On euthanasia, Mr Barnett reiterated his opposition to it, but Mr McGowan said he believed terminally ill people should be able to make their own choices.

The Labor leader drew laughs when he said he believed Christian traditions - such as Santa - should be allowed in state schools.

He got the same response when asked if he was against the sexualisation of children in outdoor advertising, saying there was too much of it in the public domain, adding that there were also too many billboards of himself and the premier around town.

"I don't think children should have to endure them," he said.