Australians have defied the warnings about voluntary voting.

Three-quarters of people have so far sent back their survey form to declare their view on marriage.

That response rate makes a lie of the warnings Australians are so used to compulsory voting that they would be too lazy to fill in an optional survey or in some way be incapable of finding a post box.

It is a clear signal that there is a strong interest in the issue, certainly enough for voters to take the required steps to not only fill in the survey but also to send it back.

The result of the vote won't be known until November 15.

Even without a result yet, this has been a success in that three out of four voters have willingly participated.

But the lengthy voting period has exposed gay people to months of public debate about whether they should be allowed to get married.

There is a view within senior ranks of the Government that the result is likely to be in favour of changing the laws to allow same-sex marriage.

That would reflect a variety of opinion polls taken over recent years showing that most Australians think same-sex marriage should be allowed.

The Prime Minister has promised that if the national vote supports changing the laws, then there would be a vote in Federal Parliament before the end of the year.

Behind the scenes, the Government is now gearing up for that vote and working towards finally bringing the long-running issue to a close.

Key dates in SSM postal survey: August 24 — the final day to register with the AEC if you want to take part in the survey

September 12 — survey forms start being sent out

September 25 — all forms are expected to have been sent

October 27 — forms are strongly encouraged to be returned by this date

November 7 — the final deadline to return surveys

November 15 — results are released

On current numbers that bill would clearly pass the Lower House and it has enough declared supporters to get through the Senate.

But there are still hurdles to clear with this lingering issue.

A few MPs have put caveats on their support and would either vote yes or "not stand in the way" if the public vote shows a "strong majority" for same-sex marriage, giving them some room to move if there is a tight result.

Debate is already raging, especially within the Coalition, about what form the bill to change the law would take.

Labor said it would support the private members bill put forward by Liberal Senator Dean Smith to allow same-sex marriage while creating exemptions so that religious organisations can refuse to conduct gay marriages.

But some MPs and Senators are determined to make those categories of exemptions much broader, opening the way for a stoush inside the Coalition party room and making existing tensions worse.

But the signs are that most Government MPs are firmly fixed on finding a way to steer this process through smoothly.

Today's figures, showing three quarters of voters have participated, give new impetus to the determination to deal with the issue this year even though the timing would be tight.