(Changes headline to show ex-general leads, not necessarily set to win)

GUATEMALA CITY, Sept 29 (Reuters) - A former general who wants to use the army to end growing violence in Guatemala is leading his center-left rival heading in to a November presidential runoff, a poll showed on Saturday.

The survey by Vox Latina said 54.4 percent of those polled who said they had decided on a candidate supported ex-Gen. Otto Perez Molina in the Nov. 4 vote, compared with 45.6 percent for economist Alvaro Colom.

About a third of voters still were undecided, said the poll, which was published in Guatemalan newspaper Prensa Libre.

Colom, a chain-smoking businessman, led Perez Molina by four percentage points the first round of voting on Sept. 9, after losing a large lead in the polls prior to the vote.

A surge in violence in one of Latin America's most crime-ridden countries appears to be helping Perez Molina, who promises to use the death penalty more often and declare a state of emergency in crime-hit areas.

More than 60 percent of those polled said crime was their top concern.

With almost 6,000 murders unsolved last year, voters appear to be putting aside concerns about Guatemala's much-loathed army -- soldiers were responsible for most of the 250,000 deaths in a 36-year civil war that ended in 1996.

Perez Molina, who commanded troops in one of the most violent areas during the civil war, was seen picking up support from voters who backed other conservative candidates in the first round.

The survey polled 1,206 people over age 18 and was conducted between Sept. 18 and Sept. 25. It has a margin of error of plus/minus 4.1 percent.

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