Political editor Malcolm Farr says vote on same-sex marriage unlikely to happen this side of the election.

THE critical vote on same-sex marriage - which spurred Kevin Rudd to dramatically declare his support - is now unlikely to go ahead next week as expected.

And it seems certain there will not be a vote on marriage equality legislation this side of the September 14 election.

It had been expected that a private member's bill for same-sex marriage, presented by Greens MP Adam Bandt in the House of Representatives in February last year, would be put to a final vote on June 6.

But there will be so many MPs wanting to speak on what is essentially a conscience issue there will not be time for a vote before Parliament rises on June 27, sources involved in the operation of the House said today.

A Greens member today suggested the Government was flinching from the prospect of former Labor leader, Mr Rudd, who supports same-sex marriage, sitting across the chamber from Prime Minister Julia Gillard and Opposition Leader Tony Abbott who oppose it.

"They don't want Kevin to sit there staring back at Julia and Tony sitting together," the Greens said.

Ms Gillard has reaffirmed her rejection of marriage reform and last week Mr Abbott said, "I certainly haven't changed my mind".

A cross-party committee which selects the legislative agenda will report its decisions tomorrow but the Bandt bill is not expected to be made a priority.

However, Mr Bandt's office will today press for priority to be given to his legislation.

Coalition MPs must vote with the party against gay marriage while Labor MPs and independents are free to vote as they wish. A ballot last September on similar legislation from a Labor MP was soundly defeated 98-41.

Mr Rudd's switch on the issue last week has given marriage equality supporters hope that others will follow and see the Bandt bill passed.

But a senior source said today, a "whole lot of people haven't spoken on this bill".

"The vote happens after everyone has a contribution, particularly on a conscience vote issue. So there was debate yesterday and there will be a need for more debate," the source said.

At least one advocate of same-sex marriage is critical of the Greens tactics which he said had prevented the legislation coming to a vote earlier.

Mr Bandt said a poll showing national support of same-sex marriage was further encouragement to push his legislation to a vote.

The Roy Morgan Poll showed 65 per cent of voters backed same-sex marriage compared to 35 per cent opposing it.

There were 70 per cent of women and 59 per cent of men listed as supporters, and 79 per cent of all voters wanted Parliament to pass legislation for same-sex marriage, Roy Morgan found.