The bill passed the capital's local assembly 39-20 to the cheers of supporters who yelled: "Yes, we could! Yes, we could!"

Leftist Mayor Marcelo Ebrard of the Democratic Revolution Party is widely expected to sign the measure into law.

The bill calls for changing the definition of marriage in the city's civil code. Marriage is currently defined as the union of a man and a woman. The new definition will be "the free uniting of two people."

The change would allow same-sex couples to adopt children, apply for bank loans together, inherit wealth and be included in the insurance policies of their spouse, rights they were denied under civil unions allowed in the city.

"We are so happy," said Temistocles Villanueva, a 23-year-old film student who celebrated by passionately kissing his boyfriend outside the city's assembly.

Only seven countries allow gay marriages: Canada, Spain, South Africa, Sweden, Norway, the Netherlands and Belgium. U.S. states that permit same-sex marriage are Iowa, Massachusetts, Vermont, Connecticut and New Hampshire.

Argentina's capital became the first Latin American city to legalize same-sex civil unions in 2002 for gay and lesbian couples. Four other Argentine cities later did the same, and as did Mexico City in 2007 and some Mexican and Brazilian states. Uruguay alone has legalized civil unions nationwide.

Buenos Aires lawmakers introduced a bill for legalizing gay marriage in the national Congress in October but it has stalled without a vote, and officials in the South American city have blocked same-sex wedding because of conflicting judicial rulings.

Many people in Mexico and elsewhere in Latin America remain opposed to gay marriage, and the dominate Roman Catholic Church has announced its opposition.

City lawmaker Victor Romo, a member of the mayor's leftist party, called it a historic day.

"For centuries unjust laws banned marriage between blacks and whites or Indians and Europeans," he said. "Today all barriers have disappeared."