Instead of the debate being held immediately - which would have seen the bill defeated --the gay marriage campaign has changed focus to increase pressure on Tony Abbott to change his mind and allow opposition MPs a conscience vote.

``The Coalition went to the last election as the party promising more individual freedom and less government interference in home life. Those values are consistent with a conscience vote on marriage equality,'' the national convener of Australian Marriage Equality, Alex Greenwich, said.

The Greens senator Sarah Hanson-Young is likely to gain opposition support for an inquiry into gay marriage legislation when Parliament returns this week.

``A Senate inquiry will provide an opportunity to address the concerns of undecided and conflicted MPs, especially on issues like guaranteeing religious freedom and the drawbacks of civil unions,'' Mr Greenwich said.

Gay marriage advocates will meet opposition MPs this week to try to put pressure on the Opposition Leader to reverse his decision not to allow Coalition members a conscience vote.

There is a pragmatic view within the Coalition that it would be best to resolve the issue once and for all while Labor is in government.

Some Coalition MPs believe that if legislation is defeated this year it would be reintroduced at some point in the future and, assuming the Coalition wins the next election, they do not want to be dogged by the issue in government as Labor was last year.

Labor MP Stephen Jones, the author of a private member's bill to legalise same-sex marriage, declined to comment on the timing of his bill.

The bill is likely to be introduced in late March.

Even if Mr Abbott allowed a conscience vote it is uncertain whether there would be sufficient support within the Coalition for legislation to pass. But Mr Greenwich believes enough MPs are supportive of change.

``Based on the unstoppable momentum for a reform that continues to win hearts and minds in the wider community and the parliament, marriage equality could be a reality in 2012,'' he said.

Labor has adopted marriage equality as its official policy, but granted a conscience vote to its MPs.