By Luis Jaime Acosta
BOGOTA (Reuters) - Colombia's Liberal Party, which won more seats than any other in the lower house and the third most seats in the Senate in recent legislative elections, on Wednesday threw its weight behind center-right presidential candidate Federico Gutierrez.
Party alliances could help push candidates over the line in the May 29 contest and are likely to affect the eventual winner's ability to push through legislation when their term starts in August.
Leftist Gustavo Petro - a former guerrilla who was later elected to congress and as mayor of capital Bogota - leads opinion polls ahead of what will likely be a first round of voting.
In recent surveys he is also tapped as most likely to win in a possible second round in June.
Gutierrez, a former mayor of Colombia's second city Medellin, is second in support, climbing in the polls since winning his coalition's primary in March.
"We are in total agreement that we must dedicate ourselves to the vulnerable, poor, marginalized people of this country, to the indigenous, the Afro-descendants, to young people," former president and Liberal Party chief Cesar Gaviria said in a statement.
Gutierrez has agreed to include anti-poverty and social development efforts in his potential government's agenda, Gaviria said, as well as boost education and health services.
Petro, who recently met with Gaviria and courted Liberal support, criticized the party for supporting his rival.
"Cesar Gaviria has decided to stick to his logic, joining with neo-liberalism to protect the rights of businesses and privatize public services," Petro said in a video message.
Despite their party's backing of Gutierrez, a group of 15 Liberal Party lawmakers have pledged their support to Petro.
Backing from the Liberals and the Conservative, U and Radical Change parties would guarantee a majority in congress for Gutierrez if he is elected, but would likely complicate Petro's planned legislative agenda if he were to win.
(Reporting by Luis Jaime Acosta; Writing by Oliver Griffin; Editing by David Gregorio)