Toronto ? Canada’s Supreme Court on Thursday declared same-sex marriages constitutional, underscoring the sharp contrast on the issue between Canada and the United States.

The court gave the go-ahead to Parliament to pass a national law legalizing gay marriage, a step that has strong public support in Canada. If the law passes, Canada would join Belgium and the Netherlands as the world’s only countries to fully legalize such unions.

Lower court rulings had upheld gay marriage in most Canadian provinces, leading to thousands of such weddings. Many have been between Americans who traveled to Canada.

The court opinion Thursday is the latest sign that Canada is on a different track than its southern neighbor, where referendums banning gay marriage passed in 11 states last month and President Bush has said he would seek a constitutional amendment to prevent gay marriage from being imposed by “activist judges” and the “far-left minority.”

Fight promised

Prime Minister Paul Martin of the ruling Liberal Party said Thursday he would introduce the gay marriage legislation early next year. Opponents promised a spirited fight in Parliament.

“We have to protect marriage,” said Gwendolyn Landolt, national vice president of Real Women of Canada, a group opposed to gay marriage, addressing reporters after the decision. “Those Liberal members of Parliament have to know they are not going to be re-elected” if they vote for the measure, she said.

Martin said he expected the measure to pass. “I’ve always thought Canada is the most postmodern country,” he told reporters in Ottawa.

Toronto’s annual Gay Pride Day parade draws hundreds of thousands of people, including nearly every successful or aspiring politician. Gay partners of Canadian military personnel get spousal benefits. Openly gay men occupy cabinet seats and other top government posts with barely a shrug about it from the public.

Kevin Bourassa, left, and Joe Varnell, the first North American gay couple to claim to be married, embrace during a celebration of the Supreme Court of Canada's opinion affirming the legality of same-sex marriage.

The opposition Conservative Party opposes religious marriage of gay partners, but supports legal civil unions between same-sex partners.

“Canada is without a doubt one of the best — if not the best — places to live as a gay or lesbian person,” said Douglas Elliott, a Toronto lawyer involved in the Supreme Court case and president of an international association that monitors laws on gays. “It’s hard to believe that just a river separates us from the reality in the United States.”

Quick change

The situation in Canada has changed quickly in a country that many people used to consider more socially conservative than the United States, gays here say.

Eleven years ago, Charles Schouwerwou and William Shannon were refused a marriage license in Ontario. “The experience at City Hall was embarrassing. The clerks were horrified when we walked up to the desk,” Schouwerwou recalled. “The woman started sputtering. She said, ‘Oh, you can’t do that.’ “

This May, Schouwerwou, 44, and Shannon, 57, his partner of 17 years, went back to City Hall. “We were treated with incredible respect,” Schouwerwou said. “There wasn’t a bat of the eye. The clerk congratulated us. It was a warm feeling, except the form still has the words ‘bride and groom.’ They need to work on that.”

“I think as a country and society, we have grown up a lot,” said Schouwerwou, a conference planner in Ottawa. “We’ve gone from a society with fears and misgivings, to where same-sex couples are commonplace. We are taxpayers, we are parents, we are politicians.”

No place in the bedroom

Gays used to envy the freedoms in the United States, said Elliott, 48, who reflected on the changes in Canada on the eve of the Supreme Court opinion. “In the ’70s and ’80s, the police chief was kicking down the doors of bathhouses, and Anita Bryant came to Canada to say that gays were a threat to children,” he said. “It was very, very scary.”

Elliott said the seeds of change were planted by Prime Minister Pierre Trudeau in the late 1960s. “He came up with the wonderful phrase that the state has no place in the bedrooms of the nation. He persuaded us that if we wanted to be a modern country in a modern world, we had to embrace separation of church and state.”