THE institution of marriage is being threatened by heterosexual couples who don't stay together, not gay marriage, Malcolm Turnbull says.

As a vote on the contentious issue was stalled until at least the end of the year, the Opposition frontbencher said he found some of the arguments against change "ridiculous''.

His comments today came as MPs in a cross-party inquiry into two bills that would change the definition of marriage failed to agree on a way forward.

Opposition members of the inquiry said they had promised voters no changes to the important institution, while Labor chair Graham Perrett said two in three people wanted it.

But Mr Turnbull, who was not on the committee, said he would be "quite untroubled by the state recognising same-sex couples and giving that the term of marriage'', although he would follow a party directive to vote against new laws.

"I have to say to you, I find the argument that the institution of marriage is under attack from homosexuals wanting to live together as quite ridiculous,'' Mr Turnbull told Sky News, adding he would likely support changes if he were allowed a free vote.

"The institution of marriage in our society is under attack, or under threat if you like, by parties to marriages, heterosexuals, lacking the commitment to stick with their marriages.

"It's the breakdown of marriage.''

He said church leaders should be out telling people to "stick together, don't commit adultery ... for god's sake, men and women of Australia, don't get divorced''.

His comments follow services on Sunday in which church leaders criticised gay marriage.

Labor MP Stephen Jones and Greens MP Adam Bandt, who have each put forward their own bills to change the marriage act, said they would try to sway enough MPs before calling a vote.

Both said they would seek out a Coalition MP brave enough to co-sponsor changes.

But some supporters, like Mr Perrett, doubted a successful vote could happen this term, although he said it should.

"It is important to remember that God did not write the Marriage Act,'' Mr Perrett wrote in his forward to the report.

"It is written by lawyers and legislators and must reflect the views and values of today.''

The Queensland MP, who has two gay brothers, said he had been told he would "rot in hell'' for his stance.

"I don't want to be lead float in the mardi gras parade. This is just me doing my job,'' he said.

Mr Bandt said he was still hopeful Opposition Leader Tony Abbott would allow his MPs a free vote, as Labor had done.

marszalekj@heraldsun.com.au



Originally published as Marriage threatened by divorce, not gays