Prime Minister Malcolm Turnbull insists same-sex marriage legislation will "sail" through parliament if a plebiscite on the issue is successful.
Mr Turnbull says he has no doubt the legislation would pass parliament, despite MPs and senators being given a free vote on the matter.
"I know parliamentarians... and I know my colleagues well enough," he told ABC's 7.30 Report on Friday.
"I have no doubt it will sail through the parliament - that is the last thing to be concerned about."
Mr Turnbull pointed to the example of Treasurer Scott Morrison, an advocate for traditional marriage, who has indicated he'd back legislation if a plebiscite voted in favour of same-sex marriage.
As for critics who say the plebiscite would open up a hateful conversation and lead to abuse of gay Australians, Mr Turnbull questioned why there weren't similar concerns about a referendum for constitutional recognition of indigenous Australians.
"Nobody is suggesting we can't have a respectful debate about that."
The coalition intends to hold a plebiscite by the end of the year if it wins on July 2.
But conservative Liberal senator Eric Abetz is reluctant to say whether he would support a peoples' vote to legalise same-sex marriage.
He said it was too early to assume Australians backed marriage equality.
"There are too many hypotheticals at this stage for me to lock myself in," he told AAP in Launceston.
"To ask people to determine what they might do at the end of the plebiscite is highly hypothetical."
Senator Abetz queried why no-one was asking gay marriage supporters if they would vote no in parliament if the plebiscite was unsuccessful.
It was vitally important both sides be given a fair go and not have one side shouted down.
Greens senator Robert Simms said it was difficult for Mr Turnbull to justify spending $160 million on a "giant opinion poll that isn't even binding on his own members".
