OTTAWA - Parliament endorsed gay marriage yesterday, rejecting by a tiny margin a 137-year-old definition that preserves the institution for "one man and one woman to the exclusion of all others."

MPs voted 137-132 against a Canadian Alliance motion to maintain the traditional meaning, despite a string of court rulings to let gays and lesbians wed.

The vote is not binding, but it is considered significant because it is the first test of a federal bill that would make Canada only the third country in the world to legalize gay marriage, after Belgium and the Netherlands.

All 63 Alliance MPs voted to keep marriage the way it is. They were joined by 53 of the 150 Liberals who turned up to vote, 10 of 14 Tories, three of 23 Bloc Qubcois MPs and three of four independents.

Twenty-nine MPs did not vote. For example, Bev Desjarlais, NDP MP for Churchill and an opponent of gay marriage, stayed away to avoid breaking ranks.

The 53 Liberal MPs who voted for the motion ignored last-minute pressure from Jean Chrtien and Martin Cauchon, the Justice Minister, to side with the government.

"You can no longer bully the caucus and you have to persuade them and if you cannot persuade them, you're going to have some difficulty with legislation," said John McKay, the Liberal MP for Scarborough East.

Mr. Cauchon appeared undaunted by the fault lines in the Liberal caucus. "We've won the vote, I think it's one of confidence in the process we've taken," he said. "Society evolves and tonight you have a good demonstration."

Paul Martin, who is expected to replace Mr. Chrtien as prime minister early next year, was among those who voted against the motion. "This is an issue that I've had to wrestle with and I must say this has not been an easy decision," said Mr. Martin, a devout Catholic.

"What has certainly tipped the balance as far as I'm concerned is the decision that the courts have taken is that this is a rights issue and you cannot discriminate."

Mr. Martin said he does not believe marriage will be eroded by including homosexuals.

Mr. Chrtien voted for an identical Alliance motion four years ago, as did most Liberal MPs, including Mr. Cauchon. That vote passed by 216-55.

When asked yesterday why he had changed his vote, Mr. Chrtien said: "On ... equality of rights, the courts spoke. I am a great defender of the Charter of Rights."

The Alliance failed in a last-minute bid yesterday to remove a contentious clause urging Parliament "to take all necessary steps" to keep the traditional definition of marriage.

A vote to soften the motion failed 135-134, after the Speaker of the House of Commons broke a tie for the first time in 40 years.

Mr. Chrtien had used the clause to persuade Liberals to defeat the motion, warning it would amount to authorizing Parliament to use the Constitution's controversial notwithstanding clause, which allows politicians to override court rulings dealing with the Charter of Rights.

But Stephen Harper, the Alliance leader, said of the bill: "If it does not pass today, it will tell the people of Canada they need a new government."

Mr. Harper speculated that his party might have secured enough votes to win, if it had succeeded in its attempts to water down the motion.

"We know that the opinion of the country is divided, and I think that's reflected somewhat in the vote," Mr. Harper said. "The other thing to note is we didn't win because some of the well-known supporters of our position didn't show up to vote as well, and I think there's going to have be some accountability."

While the Alliance accused the Liberals of changing their political stripes with ease, many government members said they switched sides because they have been swayed by court rulings.

Courts in British Columbia, Ontario and Quebec have struck down the federal ban on gay marriage as a violation of the equality guarantees in the Charter.

A federal bill legalizing same-sex marriage has been sent to the Supreme Court of Canada for a legal opinion on whether it passes constitutional muster before it is introduced in the House of Commons.

The traditional definition of marriage is based on an 1866 court ruling in England, in which Lord Penzance wrote: "I conceive that marriage, as understood in Christendom, may ... be defined as the voluntary union for life of one man and one woman, to the exclusion of all others."

Despite Mr. Martin's vote, he refused to commit to the bill legalizing gay marriage, should he become prime minister.

"There are a number of options that have been put on the table," he told reporters.

He said that final answer must comply with the Charter of Rights, which rules out a "separate but equal" regime for gays and lesbians.

Mr. Martin did, however, muse about registered civil unions, but the prospect already has been rejected by the Ontario Court of Appeal on the grounds that it still shuts same-sex couples out of marriage.

Some proponents of civil unions have suggested the government should get out of the marriage business altogether by bringing in civil unions for everybody who does not choose to marry in a church.

Mr. Harper kicked off yesterday's divisive debate by rejecting Liberal claims that gay marriage is a civil rights issue akin to racial segregation.

"For the Liberals or anyone in the Liberal party to equate the traditional definition of marriage with segregation and apartheid is vile and disgusting," said the Alliance leader, who was accused by his political opponents of being homophobic.

In another bitter exchange, Vic Toews, the Canadian Alliance justice critic, denounced the strong views of gay MP Svend Robinson by saying "his ideology is fascism, not free speech."