MEXICO CITY — Mexico City lawmakers on Monday made the city the first in Latin America to legalize same-sex marriage, a change that will give homosexual couples more rights, including allowing them to adopt children.

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 was widely expected to sign the measure into law.

Mexico City's left-led assembly has made several decisions unpopular elsewhere in this deeply Roman Catholic country, including legalizing abortion in the first 12 weeks of pregnancy. That decision sparked a backlash, with the majority of Mexico's other 32 states enacting legislation declaring life begins at conception.

The conservative Nation Action Party of President Felipe Calderon has vowed to challenge the gay marriage law in the courts. However, homosexuality is increasingly accepted in Mexico, with gay couples openly holding hands in parts of the capital and the annual gay pride parade drawing tens of thousands.

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.

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

"They have given Mexicans the most bitter Christmas," said Armando Martinez, the president of the College of Catholic Attorneys. "They are permitting adoption (by gay couples) and in one stroke of the pen have erased the term 'mother' and 'father."'

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."