THE message from nervous politicians in Canberra was not so much "I do" as it was "not yet" on the divisive question of same-sex marriage.

Such was the inconclusive result of a parliamentary inquiry into two Bills to alter the definition of marriage - one from Greens deputy leader Adam Bandt, the other from Labor MP Stephen Jones.

MPs are divided largely on party lines, even though the chair of the House of Representatives' Social Policy and Legal Affairs Committee, Graham Perrett, advocated change to allow the equal recognition of same-sex relationships.

Formally, the committee elected not to take a position but proposed changes to the Bills to improve their wording.

It urged Parliament to dump specific references to "sexual orientation or gender identity" in one of the amendments, replacing them with less confronting words: "The object of this Act is to amend the Marriage Act 1961 to ensure equal access to marriage for all couples who have a mutual commitment to a shared life."

Mr Perrett, who has gay siblings, said it was the quality of a relationship that mattered.

"It is timely for me to remind everyone that God did not write the Marriage Act," he told Parliament. "It was written by lawyers and legislators - in ink, not stone."

Mr Bandt said the principle of equality was vital but conceded the numbers for a law change were not yet there in Parliament. "It should be done not just because it's popular but because it is right," he said.

While Labor MPs will be free to follow their conscience if the matter comes to a vote, Coalition MPs will not. Both Tony Abbott and Julia Gillard oppose any change.

The Australian Christian Lobby welcomed the committee's refusal to endorse either amendment.

"The committee report also confirmed that there is no substantive discrimination against homosexual couples," managing director Jim Wallace said. "This confirms the retention of the definition of marriage is rightly a matter of biology and there is no discrimination that justifies it being changed."