BRASILIA (Reuters) - President Dilma Rousseff holds a clear lead ahead of Brazil's election in October, but her main rivals are closing the gap as voters begin to decide who to back, according to a poll published on Thursday.
While Rousseff still has enough of an advantage to win re-election in a first round vote if it were held today, her opponents gained more ground from growing media exposure as the campaign begins to shift gear, making a run-off more likely.
Left-of-center Rousseff has stemmed the decline in her popularity caused by high inflation and a political scandal involving management of state-run oil company Petrobras.
Voter support for Rousseff recovered to 40 percent in May from 37 percent in a previous poll in April, the local IBOPE polling firm said.
But her main rival, Aécio Neves of the centrist PSDB party, rose to 20 percent from 14 percent in April, while Eduardo Campos, the candidate of the Brazilian Socialist Party, advanced to 11 percent from 6 percent the month before.
Added together, Neves, Campos and other possible candidates now have 36 percent of eligible votes, reducing the gap with Rousseff to just four percentage points, from 13 points a month earlier. Rousseff needs to wins more than all other candidates put together to avoid a run-off.
The election campaign heated up last week with combative video by Rousseff's ruling Workers' Party that focused on how life has improved for Brazil's poor since it came to power in 2002 and warning voters that those social gains could be lost.
While campaigning will not start officially until after the soccer World Cup ends in mid-July, little known opposition candidates have gained support by stepping up their public appearances and media interviews.
Undecided voters have dropped to 10 percent from 14 percent a month earlier, while the number of people who said they would not vote on October 5 has fallen from 24 percent to 14 percent, the IBOPE poll said.
The poll, published by Globo TV News and O Estado de S.Paulo newspaper, interviewed 2,002 eligible voters between May 15 and 19 and has a margin of error of plus/minus 2 percentage points.
(Reporting by Anthony Boadle; Editing by Chizu Nomiyama)