By Nelson Renteria and Anahi Rama SAN SALVADOR, Feb 2 (Reuters) - A former left-wing guerrilla commander faced-off against a conservative rival who wants to send the army in to fight powerful street gangs in El Salvador's presidential election on Sunday. Salvador Sanchez Ceren, a rebel commander who became a top leader of the leftist Farabundo Marti National Liberation Front (FMLN) during El Salvador's civil war, went into the election with a solid lead over Norman Quijano, who stepped down as the mayor of San Salvador, the capital, to run, polls showed. But with three main candidates competing, Sanchez Ceren was widely expected to fall short of the more than 50 percent support needed to win outright. If there is no clear winner on Sunday, the two leading candidates will go to a run-off on March 9. Sanchez Ceren held a lead in the polls after El Salvador's first leftist government, elected in 2009, established social welfare programs such as free school supplies that were a popular balm for the one third of the country that lives in poverty. "The Front is going to win because of the poor. They are giving us opportunities. My kids would not have been able to study without their help," said housewife Patricia Concepcion, 43, as voting wrapped up. Any run-off would turn distant third-place candidate Antonio Saca, who was president from 2004 until 2009, into a potential kingmaker. After leaving office, Saca broke away from Quijano's Arena party. Some of Saca's supporters are conservative and could migrate to Quijano in a second-round vote, but others may turn to Sanchez Ceren. The FMLN turned into a political party at the end of the civil war, and Sanchez Ceren has tried to appeal to moderate voters in this campaign as he looks to keep his party in power. But the tight race reflects a deep divide that dates back to the brutal 1980-1992 civil war, which killed 75,000 people, and sluggish economic growth has contributed to the surge of violent street gangs. Quijano is the candidate of the right-wing Nationalist Republican Alliance (Arena) and is promising tough policies to crack down on the gangs. "It is just terrible. You can't even leave your house because there is danger everywhere. It is time to put and end to this," said Sandra Marin, 40, a shoe saleswoman. Sanchez Ceren rejects the idea of deploying the army to fight the gangs and instead vows to forge a political pact to break through gridlock that has kept a divided Congress from carrying out reforms to tackle crime and weak economic growth. "More than ever we need a new national accord, so that we do not have partisan policies but policies that are backed by all the people of El Salvador," he said after voting on Sunday. Sanchez Ceren started out as a rural teacher and rose to become a top rebel leader during the civil war, when the FMLN fought a string of U.S.-backed conservative governments. He attended a mass early on Sunday at the chapel where Archbishop Oscar Romero was assassinated at the start of the civil war. Romero, who denounced oppression of the poor by country's military dictators, is a hero of the left. The FMLN won power at the last election when it put up a popular journalist, Mauricio Funes, as its candidate. He had no role in the civil war and has led the FMLN toward more moderate leftist policies. TRUCE Although many Salvadorans are terrified of the street gangs, a two-year-old truce between the Mara Salvatrucha (MS-13) gang and its rival, Barrio 18, has helped cut the number of murders in half from one of the highest homicide rates in the world to a 10-year low in 2013. A victory by the right could disrupt that fragile truce if the military is used to battle the gangs. Quijano, a 67-year-old former dentist who became San Salvador's mayor, accused the FMLN of making deals with gangs to win votes in areas controlled by the criminal groups after he voted in a Roman Catholic school's basketball gym amid supporters waving blue, white and red Salvadoran flags. "Do you want to stay with a government that makes deals with criminals?" Quijano said. "Or do you want a capable person, determined and with a clean record?" Orlando Sanchez, a 73-year-old bricklayer, believes Arena, which was founded by members who backed death squads during the civil war, would steal public money if it regains power. "This country is poor because they left it that way," he said as he walked in a park in the capital's historic center. El Salvador's economy is heavily reliant on money sent home by migrants living and working in the United States.