SAN SALVADOR, Jan 19 (Reuters) - El Salvador’s leftists had a strong showing in congressional elections, boosting momentum for the party of former Marxist guerrillas that is seeking the presidency, vote tallies showed on Monday.

With nearly 70 percent of the ballots counted from Sunday’s polls, the Farabundo Marti National Liberation Front had 49.5 percent of the vote in the National Assembly, versus 40 percent for the ruling right-wing Nationalist Republican Alliance, or ARENA.

The results give FMLN presidential candidate Mauricio Funes, a former TV journalist, a better chance of taking the presidency in a March election.

The latest survey in December gave the center-left former CNN journalist a 16 percentage point lead over ruling ARENA candidate Rodrigo Avila, El Salvador’s former police chief.

Funes reported on El Salvador’s 12-year civil war but never fought in it and was not a Marxist guerrilla.

Since the Cold War era conflict ended with 1992 peace accords, the FMLN has lost three presidential elections to ARENA. The FMLN’s violent past has kept it from winning the presidency, analysts say.

But ARENA has struggled to curb gang violence and convert economic growth into gains for the poor. It is also unpopular for supporting the U.S.-led war in Iraq and sending troops there.

Funes promises to pursue market-friendly policies and get on well with Washington if he wins. He appeals to pro-U.S. voters who never before supported the FMLN.

Funes’ opponents fear El Salvador will join a left-wing bloc of Latin American countries led by Venezuela if he wins, but he dismisses the claims and the party faithful have dropped much of the anti-American rhetoric of the past.