Gay marriage on Labor conference agenda

Federal Labor looks set to back gay marriage as the party's national conference gets under way in Sydney.

The gathering of 400 ALP delegates begins in Sydney on Friday with jobs, the economy, education, families and climate change on the agenda on the first day.

But on Saturday, debate will turn to the issue of changing the federal Marriage Act to allow same-sex couples to wed.

Prime Minister Julia Gillard said during the 2010 election she stood by the definition of marriage being between a man and woman, which is the stance in the party's current platform.

But the Right faction on Thursday endorsed the prime minister's plan for a conscience vote in federal parliament and will take it to the conference on Saturday.

While ACT Deputy Chief Minister Andrew Barr, a member of the faction, welcomes the conscience vote, he argues the party should go further and change its platform.

He says he's confident a motion - seconded by federal minister Penny Wong, from the Left - will get the more than 200 votes it needs to succeed.

Social conservatives in the Right faction have yet to come up with an alternative wording for the platform, but have conceded the conference will vote for change.

Proponents have gained confidence after the Queensland parliament passed laws allowing same-sex civil unions in the state, mirroring the arrangements already existing in the ACT, Victoria and Tasmania.

During the conference, both sides of the gay marriage debate will present petitions with more than 100,000 signatures each.