GAY marriage has been rejected by the majority of MPs who took part in a special parliamentary debate on the issue.

But some MPs who oppose redefining the term marriage have backed civil unions to lessen discrimination faced by same-sex couples.

The debate on gay marriage was forced by Melbourne Greens MP Adam Bandt, who wanted politicians to survey their electorates on the subject.

Some of the 30 MPs who took part in the debate attacked Mr Bandt for "distracting" from other issues such as the carbon tax and jobs.

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Most MPs who took part in the debate said their electorate did not support gay marriage, while just six said that their electorate supported change.

Several Labor MPs spoke in favour of gay marriage, with the issue to be debated at the party's national conference later this year.

Labor MP Graham Perrett, who is Catholic and has two gay brothers, said gay marriage would help protect people from discrimination.

"Too many constituents told me their children were bullied and belittled because they were same-sex attracted. Some were even driven to suicide," he said.

"I cannot sit idly by while the nation is complicit in this harm."

Several MPs who opposed gay marriage, including Victorian Liberals Bruce Billson and Josh Frydenberg, said a move towards civil unions was more practicable.

Mr Billson said he thought a phrase such as "committed life partnership" would be better than "civil union", however.

Labor MP John Murphy said he had been abused by some constituents as a "bigot" after he opposed same-sex marriage.

Nationals senator Ron Boswell, who was not part of the debate because he is not an MP, produced a petition with more than 55,000 signatures of people opposing a change to the marriage definition.

That was countered by Left-leaning lobby group Get Up! that produced another petition with a similar number of signatures of people in support of gay marriage.

As far as Mr Bandt, who started the debate, is concerned all that matters is love. "I am confident that it will not be long before marriage equality will be achieved because love builds bridges where there are none," Mr Bandt said.

johnstonm@heraldsun.com.au

Originally published as MPs reject gay marriage, support civil union