By Nelson Renteria and Michael O'Boyle SAN SALVADOR, Feb 3 (Reuters) - A former Marxist guerrilla leader is in a strong position to win El Salvador's presidential election in a run-off against his right-wing rival after falling just shy of an outright win in the first round of voting on Sunday. Salvador Sanchez Ceren, a top leader of the Farabundo Marti National Liberation Front (FMLN) rebel army during El Salvador's civil war, won 48.9 percent of votes in the first round, just short of 50 percent needed to avoid a run-off. He will now face off on March 9 against Norman Quijano, the conservative former mayor of San Salvador, who won 38.95 percent of the vote and wants to deploy the army to fight powerful street gangs. The FMLN turned into a political party at the end of El Salvador's 12-year civil war in 1992, and it won power at the last election in 2009. Sanchez Ceren was vice-president in the government and his campaign was helped by its popular welfare policies, including pensions and free school supplies. "We won the first round ... we are sure that in the second round we will win by more than 10 points," the 69-year-old Sanchez Ceren told cheering supporters on Sunday night. "We are going to work in the coming days to further unite," he added. "We are going to build new understandings, new alliances." Sanchez Ceren appears to be in a very strong position ahead of the run-off. The third-place candidate Antonio Saca, who was president from 2004 until 2009, had about 11.4 percent support. After he left office, Saca broke away from Quijano's Nationalist Republican Alliance (Arena) party. It is unclear whether he will throw his support behind Sanchez Ceren in the run-off or who his supporters will back. The Universidad Centroamericana estimates that while most of Saca's supporters would likely opt for Quijano in a run-off, around 25 percent would go with Sanchez Ceren, giving him enough for victory. A Sanchez Ceren presidency would boost the influence of Venezuela's socialist government as he has said he will seek to join the South American oil giant's Petrocaribe oil bloc, which furnishes allies, often leftists, with cheap energy. POVERTY, VIOLENCE More than two decades after the end of the civil war, El Salvador remains deeply divided between left and right and the rise of violent street gangs has been spurred by persistent poverty and sluggish economic growth. The country is more reliant on money sent home by migrants working in the United States than any other country in Central America. Those remittances make up nearly 20 percent of gross domestic product. Quijano's main campaign pledge has been to deploy the army against the street gangs. Sanchez Ceren opposes the idea and is instead promising to forge a political pact to end the gridlock that has kept a divided Congress from carrying out reforms to tackle crime and weak economic growth. He also promises to fight tax evasion and eliminate loopholes while introducing tax incentives to boost investment in key industries, such as energy, and to renovate the capital's airport and improve port facilities. He was a rural teacher before the civil war but joined the FMLN and became one of its leading commanders as it fought a series of U.S.-backed conservative governments. About 75,000 people were killed in the 12-year conflict. The FMLN has steadily won more supporters as it has toned down some of its more radical left-wing policies and it won power in 2009 when it put up a popular journalist, Mauricio Funes, as its candidate. Unlike most FMLN leaders, Funes had no role in the civil war. Sanchez Ceren's candidacy was seen by some as a risky move but he has stressed his desire for national agreements with the other parties and named a popular moderate as his candidate for vice president.