By Anthony Boadle
BRASILIA, Feb 18 (Reuters) - Protests during the World Cup and the rising cost of living could undermine support for Brazil's President Dilma Rousseff and endanger her chances of re-election this year, according to a poll released Tuesday.
Rousseff remains the clear front-runner to win the October 5 vote, according to a survey by local polling firm MDA. Her personal approval rating slipped to 55 percent this month from 58.8 percent in November, when MDA last conducted a poll. At that time, her popularity was recovering from a sharp decline following massive protests against corruption and poor public services.
More Brazilians intend to vote for Rousseff than for her two potential rivals together, according to the new poll. But as many as one-third of voters are undecided, and it is too early to say whether she can win the election outright or face a runoff.
"In my view, there will be a second-round vote," said Senator Clésio Andrade, president of the industry group National Transport Confederation, which commissioned the poll.
"There is pessimism setting in. She should watch out for the health issue, rising prices and the big demonstrations that we expect," Andrade said at a news conference, referring to the top three issues worrying Brazilians who were surveyed.
Brazilian authorities are bracing for an outburst of protests during the World Cup soccer tournament that the country will host from June 12 to July 13, especially in the 12 cities where teams from 32 nations will play matches.
More than three-fourths of Brazilians believe the billions of dollars spent on World Cup stadiums was an unnecessary expense, and 80.2 percent think the money should have been used on other priorities, the CNT/MDA poll indicated.
The survey showed that the main problems worrying Brazilians include poor health services (84.4 percent of those polled) and the low quality of education (47.6 percent), along with rising consumer prices, which is a major concern in a country with a history of runaway inflation.
Three out of four Brazilians say that the cost of living went up in the last 12 months and will continue to do so this year, with food prices seen as the main culprit. Complaints about exorbitant prices have gone viral on Brazilian social media, with several online communities dedicated to denouncing prices charged by bars and restaurants.
High inflation has dented consumer spending, which until recent months had been one of the few growth engines for the Brazilian economy, now in what is expected to be its fourth straight year of lackluster growth.
MDA pollster Marcelo Costa Souza said the drop in Rousseff's personal approval rating was statistically insignificant since it fell within the poll's margin of error of 2.2 percentage points in either direction.
The survey, however, showed that 37.3 percent of those surveyed had a negative view of the left-leaning Rousseff among the potential presidential candidates.
Massive protests badly damaged Rousseff's popularity in June, when more than a million Brazilians took to the streets to demand an end to political corruption, more transparent government and better use of public resources. Her personal approval rating sank from 73.7 percent in June to 49.3 percent in July.
In the latest poll, 43.7 percent of those surveyed said they intend to vote for Rousseff, compared to 43.5 percent in the previous MDA survey in November.
Her main rival, Aécio Neves of the centrist Brazilian Social Democracy Party, had 17 percent support in the poll, slipping from 19.3 percent in November.
Eduardo Campos, the governor of Pernambuco state and a former Rousseff ally who is mounting a run for the presidency, advanced slightly to 9.9. percent from 9.5 percent.
The poll showed environmentalist and former presidential candidate Marina Silva would be Rousseff's toughest rival if she were to run instead of Campos, whose Brazilian Socialist Party she joined last year after failing to register her own party in time.
MDA surveyed 2,002 registered voters from Feb. 9-14. (Editing by Todd Benson and Amanda Kwan)