A CONSCIENCE vote on same sex marriage in Federal Parliament is unlikely to sway the views of WA Liberals who vehemently oppose the idea.

Even openly gay WA Liberal Senator Dean Smith yesterday opposed same sex marriage, despite federal Opposition leader Tony Abbott opening the door to allowing Liberal MP's a conscience vote on recognising the union in Australia.

The move would be a shift from the Coalition leader's previous ruling that all federal Liberal MP's vote against same marriage.

"I have not yet been convinced that we should move away from the traditional and well understood meaning of marriage,'' Senator Smith said.

(But) I strongly believe to be consistent with our party traditions a conscience vote is the most appropriate defensible course of action on the issue of same sex marriage.''

Mr Abbott last year year denied his MPs a conscience vote in parliament to amend the commonwealth Marriage Act to include same sex couples.

Prime Minister Julia Gillard, who is also opposed to same sex marriage, did give Labor MPs a vote on the issue according to their conscience - but the amendments were voted down.

While Labor federal MP's Louise Pratt, Chris Evans, Gary Gray, Stephen Smith and Melissa Parke were amongst those who supported same sex marriage when the vote was taken in federal parliament last September, Liberal MPs voted against it.

This week, Labor MPs contacted by The Sunday Times continued their support for same sex marriage, while a number of Liberals continued their opposition.

In a survey of WA federal MPs and senators by The Sunday Times this week Labor's Louise Pratt, Melissa Parke, Stephen Smith and Gary Gray continued their support for same sex marriage.

Green senators Scott Ludlam and Rachel Siewart also supported same sex marriage.

But WA Labor senator Mark Bishop opposed same sex marriage.

Liberal politicians Julie Bishop, Ken Wyatt, Mathias Cormann, Dean Smith, Steve Irons, Michael Keenan and Dennis Jensen opposed the move as did National Party MHR Tony Crook.

Liberal politicians Nola Marino, Barry Haase, David Johnston, Michaelia Cash, Alan Eggleston, David Johnston, Judi Moylan, Luke Simkins, and Dr Mal Washer declined to comment.

"This is a matter that I have consulted extensively with residents in my electorate about,'' Hasluck MHR Ken Wyatt said.

"It is a deeply personal matter for those on both sides of politics.

"The Coalition's position, which I support, is that marriage is defined by the Marriage Act is between a man and a woman.''

WA Liberal Senator Mathias Cormann said "marriage is an institution with a special status''.

"I support the view that children deserve to have the opportunity, all other things being equal, to grow up with both a mother and father.''

But lesbian WA Labor senator Louise Pratt said the vast majority of Australians supported her pro-same sex marriage stance.

"Marriage quality won't go away as an issue until it is won,'' she said.