SANTIAGO (Reuters) - Center-left lawmakers in Chile pledged on Wednesday to unify and support a single candidate in any eventual runoff against conservative candidate Sebastian Pinera, who is leading in polls for this year s presidential race.  While Pinera has consolidated support among the country s political right, six left-of-center candidates will be competing in the Nov. 19 first round vote, amid fissures within socialist President Michelle Bachelet s coalition and the emergence of new left-wing leaders.  Polls show Pinera, a wealthy businessman who previously governed Chile between 2010 and 2014, has around 40 percent of voter intentions. That would not be enough to win an absolute majority in the first round. A December runoff is expected to be closer, meaning the left s ability to unite around a single candidate could be critical.  After the first round in which each of us will give our best effort for the candidate we most support, we promise that in the second round we will support the candidate that represents the forces of the left and center-left,  some 300 politicians said on Wednesday in a letter.  Senator Alejandro Guillier, an ally of Bachelet who is polling second, has previously said he would seek links with other  progressive  candidates to ultimately defeat Pinera. Bachelet is constitutionally prohibited from seeking a second consecutive term. The Christian Democrat party, a large centrist and socially conservative party that is putting forward its own candidate, has been hesitant to pledge unity to date, following deep divisions with the governing Nueva Mayoria bloc over elements of Bachelet s policies in recent months. But one of the party s lawmakers said on Wednesday that it would support the best-performing Nueva Mayoria candidate.  The night of the 19th we are going to get behind the candidate who moves on to the second round,  Christian Democrat Congresswoman Yasna Provoste told journalists on Wednesday. 