UPDATE 2-Brazil's Rousseff widens lead in new poll
* Vox Populi poll shows Rousseff with 51 percent
* Suggests frontrunner may have stemmed bleeding
* Pool of undecided voters shrinking (Writes through, adds quote)
By Todd Benson
SAO PAULO, Oct 19 (Reuters) - Ruling party candidate Dilma Rousseff widened her lead ahead of Brazil's presidential runoff election, a poll showed on Tuesday, suggesting her campaign may be steadying after a recent slide in support.
The survey by polling firm Vox Populi showed Rousseff with 51 percent of voter percent ahead of the Oct. 31 vote compared to 39 percent for centrist opposition challenger Jose Serra, according to iG, an Internet group that commissioned the poll.
Rousseff, the handpicked would-be successor of President Luiz Inacio Lula da Silva, had 48 percent support of voters to Serra's 40 percent in the last Vox Populi poll, which was released 10 days after the Oct. 3 first-round vote.
Support for Rousseff has been consistently higher in Vox Populi's polls.
But it is still a welcome boost for her campaign after other polls indicated Serra, the former Sao Paulo state governor, had been gaining ground since Rousseff failed to win a first-round majority in the Oct. 3 election.
One poll last week showed him only four percentage points behind the left-leaning Rousseff, a statistical dead heat, while other recent surveys showed her with a lead of up to seven points.
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Amaury de Souza, a political consultant in Rio de Janeiro, said the poll suggested Serra was losing his recent momentum.
"I don't think anything's over. This is a very competitive race and whoever wins will win by a relatively small percentage," he said.
The poll showed that 4 percent of voters were undecided, down from 6 percent in the previous survey, leaving a shallower pool of wavering voters whose support is particularly crucial to Serra's chances of overtaking Rousseff.
Blank and null ballots made up 6 percent of votes in the poll, which surveyed 3,000 people between Oct. 15-17 and has a margin of error of 1.8 percentage points. With blank votes thrown out, as they are on election day, Rousseff's support rose to 57 percent versus 43 percent for Serra.
Rousseff, a 62-year-old former chief of staff to Lula, took 47 percent of the votes in the first round to Serra's 33 percent.
UPHILL STRUGGLE FOR SERRA
But Rousseff's once-smooth campaign has been shaken recently by corruption allegations involving a former aide and attacks by religious leaders over her past views on abortion, which may have cost her outright victory in the first round.
That has forced the former leftist militant to take a more aggressive tone against Serra and distracted her from her central message -- that she is the best person to continue Lula's legacy of buoyant economic growth and development.
The 68-year-old Serra, running for the PSDB party, has been re-energized by his first-round survival and rise in polls. But he was dealt a setback on Sunday when the potentially influential Green Party opted to stay neutral in the runoff.
Serra probably needs to win a large proportion of the around 20 million voters who supported third-placed candidate Marina Silva of the Green Party in the first round to have any chance of beating Rousseff.
Rousseff, the Workers' Party candidate, would be Brazil's first woman elected president and is expected to broadly continue Lula's policies. She wants to boost investment in Brazil's decrepit infrastructure and raise government efficiency but is unlikely to push the major structural reforms many economists say is needed to maintain strong growth.
Serra is also unlikely to change Lula's broad economic policies, although his rise in the polls has prompted some selling of Brazil's soaring currency -- Serra has argued that the country's high interest rates must be brought down. (Additional reporting by Stuart Grudgings; Editing by Paul Simao)