"I haven't had the opportunity to view it myself. I've seen the reports of it, but no, my view hasn't changed and when a bill comes to the parliament later this year ... I won't vote for it."

Going public ... US President Barack Obama has come out in support for gay marriage. Credit:Reuters

Asked if her progressive credentials were not measuring up, Ms Gillard replied: "Well you know, I believe what I believe ... You can judge it."

Advocates of gay marriage praised Mr Obama after he expressed support for their cause overnight, ending nearly two years of “evolving” on the issue.

He told ABC News: "Over the course of several years as I have talked to friends and family and neighbours, when I think about members of my own staff who are in incredibly committed monogamous relationships - same-sex relationships - who are raising kids together, when I think about those soldiers or airmen or marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that 'don't ask, don't tell' is gone, because they are not able to commit themselves in a marriage, at a certain point I've just concluded that for me personally it is important for me to go ahead and affirm that I think same sex couples should be able to get married."