BUENOS AIRES - Argentina was on the cusp of legalizing abortion Tuesday over the objections of its influential Roman Catholic Church, with the Senate preparing to vote on a measure that has the backing of the ruling party and already has passed in the lower house. 
 
If passed, the bill would make Argentina the first big country in predominantly Catholic Latin America to allow abortion on demand. The vote is expected to be close after what was expected to be a marathon debate, beginning at 4 p.m. local time (1900 GMT) and likely to stretch into Wednesday morning. 
 
Demonstrators both for and against the bill came from around the country to stand vigil in front of the Senate building in Buenos Aires. 

"Argentina is a pro-life country," one woman, who said she was from Cordoba province, told local television as she sat in a folding chair under an umbrella sheltering her from the Southern Hemisphere summer sun. She and others who knelt in prayer nearby said they were against the proposed change in law. 
 
Maria Angela Guerrero of the Campaign for Legal Abortion activist group, speaking to reporters in front of the Senate, said she was "cautiously optimistic" the bill would pass. 
 
On the other side of the debate is the Catholic Church, which is calling on senators to reject the proposal to allow women to end pregnancies up to the 14th week. Argentina is the birthplace of Pope Francis. 
 
Argentine law now allows abortion only when there is a serious risk to the health of the mother or in cases of rape. 
 

Legal abortion is extremely rare in Latin America because of the long history of opposition by the Church. Across the region, abortions are available on demand only in Communist Cuba, comparatively tiny Uruguay, and some parts of Mexico. 
 
The change in law has been rejected by Argentina's Congress before, but this is the first time such a bill is being presented to lawmakers with support from the ruling government. In 2018, before center-left Peronist Alberto Fernandez was elected president, a similar bill was rejected by a slim margin. 
 
The measure is accompanied by side legislation aimed at assisting women who want to continue their pregnancies and face severe economic or social difficulties.