Argentinian lawmakers voting on same-sex marriage.

STORY HIGHLIGHTS

• NEW: The Argentine Senate is debating a same-sex marriage bill
• The bill would give same-sex couples equal marriage rights and ability to adopt children
• Catholic and evangelical churches in Argentina have organized protest marches
• Thousands of protesters demonstrated in front of the Argentine Congress

(CNN) -- Debate was under way Wednesday in Argentina's Senate on a same-sex marriage bill that already has passed the lower chamber of Congress. A vote was expected later Wednesday.

The bill would give same-sex couples equal marriage rights, including the ability to adopt children.

Addressing claims that church leaders have been lobbying lawmakers about the proposal, Sen. Miguel Angel Pichetto told the state-run Telam news agency that he had not been pressured.

"There is some pressure in some provinces where the church plays a prominent role, but such is democracy," he said.

Thousands of people protested the measure Tuesday in front of Argentina's Congress in marches convened by Catholic and evangelical churches in the country.

"We don't want a negative tint, that's not the objective of the march, but to propose and promote marriage as we understand it, between a man and a woman," said Justo Carbajales, representative of the Episcopal Church in Argentina, according to Telam.

A smaller, but just as boisterous, group of counter-protesters in favor of the bill congregated in another part of the city.

On the eve of Wednesday's vote, Senate Provisional President José Pampuro told Telam that he would vote "affirmatively for gay marriage."

Last month's congressional vote and Wednesday's Senate vote are the latest moves in a pro-gay marriage trend in Argentine politics.

Last year, a judge in Buenos Aires ruled that a ban on same-sex marriage was illegal, paving the way for such marriages in the capital of Argentina. An injunction by another judge stopped what would have been the first same-sex marriage there.

Ultimately, Latin America's first same-sex marriage happened in Argentina in a southern state with a pro-gay marriage governor.

Now, the issue has reached beyond local and state politics to the national stage........By the CNN Wire Staff

July 14, 2010 -- Updated 1731 GMT (0131 HKT).