Anticipating a Supreme Court ruling endorsing his government's proposed legislation on same-sex marriage, the federal justice minister says he will move quickly to change the law.

The high court is scheduled to offer its opinion on the federal bill Thursday morning around 10 a.m. ET.

Justice Minister Irwin Cotler says that if the top court follows the example set by lower courts across the country, the governing Liberals could begin the process of turning the draft bill into law before the end of December.

"We expect that the Supreme Court will uphold the appellate and lower-court judgments in this matter,'' Cotler told reporters Wednesday after a Liberal caucus meeting.

"We expect that the two foundational principles -- namely of equality rights and religious freedom -- will be sustained.

"And therefore, based on these Charter principles, we will move ahead... with all deliberate speed to introduce legislation which will extend civil marriage to gays and lesbians.''

Lower courts in British Columbia, Ontario and Quebec got the ball rolling when they ruled same-sex marriage legal.

That prompted the government of then-prime minister Jean Chretien to draft a law to legalize the unions. The legislation would allow gay and lesbian weddings in city halls, courthouses and in religious institutions that chose to recognize them.

Before he retired, however, Chretien asked the country's Supreme Court justices to decide whether Parliament had the power to change the definition. The Court has heard arguments from both sides on the controversial case.

Ottawa has also asked the court to rule on three other questions:

• Whether the definition can legally be expanded to include gays and lesbians,
• Whether religious leaders are protected under the Charter of Rights from having to marry same-sex couples,
• And, whether the existing opposite-sex requirement for marriage is constitutional.

Under the draft legislation, religious institutions would be allowed to define marriage as they like and would not be required to perform same-sex marriages.

Following lower court rulings in Manitoba, Nova Scotia, Saskatchewan, and the Yukon, same-sex marriage is now temporarily legal in every province or territory where the constitutionality of banning it has faced a judicial test.

If the bill is approved by the court and comes to a vote in Parliament, Prime Minister Paul Martin has said Liberal backbenchers will be allowed to vote freely on it -- but he will ask them to support the bill.

But in a minority Parliament, every vote will count. Most Conservative MPs are against the bill, and many are angry that the courts have looked at the issue before they have.

"My strongly held view is that this should have been decided by elected people and not appointed people," says party leader Stephen Harper.

The NDP and the Bloc Quebecois meanwhile are walking down the aisle together on the issue, saying most in their parties like the legislation.

"Our position has always been that this is an issue of human rights. And our party was the only party to support same-sex marriage in our platform," says NDP leader Jack Layton.

If the legislation eventually passes in Parliament, Canada would be among the first countries to officially recognize gay and lesbian marriages.