* Ruling coalition's Rousseff extends lead over Serra
* Poll suggests scandal allegations having little impact (Recasts, adds details, background)
BRASILIA, Sept 14 (Reuters) - Brazil's ruling party presidential candidate Dilma Rousseff stretched her lead over her opposition rival and is on course for a resounding victory despite a series of ethics allegations against her, an opinion poll showed on Tuesday.
Rousseff has 50.5 percent of voter support against 26.4 percent for main opposition contender Jose Serra, the survey by polling firm Sensus showed. In a similar Sensus poll published on Aug. 24, Rousseff had 46 percent and Serra 28.1 percent.
Riding the huge popularity of outgoing President Luiz Inacio Lula da Silva, Rousseff appeared headed for the majority of votes she needs to knock out Serra in the first round of voting on Oct. 3.
That result, which has been predicted by all major polls in recent weeks, would remove the need for a run-off vote and give the 62-year-old former leftist militant a strong mandate to rule Latin America's largest country. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ For a factbox on political risks in Brazil: [ID:nRISKBR] For full coverage of Brazil's election: [ID:nBRAZIL] For election Top News page: link.reuters.com/dux43p For a graphic on all polls: link.reuters.com/vux47n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
Once spoiled and blank poll responses removed -- as happens with spoiled ballots in the election -- Rousseff had 57.8 percent in the Sensus poll.
"The electorate has basically decided," said Ricardo Guedes, the director of Sensus.
Former Sao Paulo state governor Serra has honed in on ethics accusations against Rousseff and her political party in recent weeks, but there are no signs that the scandals are undermining Lula's former chief of staff.
Serra, 68, accuses Rousseff and her leftist Workers' Party of having illegally accessed tax records of his daughter and opposition members to gather potentially damaging information against them.
A new scandal erupted last weekend when a magazine published accusations that one of Rousseff's former aides, who is now Lula's chief of staff, was involved in a kickback scheme for public works contracts run by her son's consulting firm.
The scandals are likely to dominate the rest of the campaign as the media digs up more details, but analysts say the lack of any evidence linking Rousseff to wrongdoing means they are unlikely to change most voters' minds.
Rousseff is widely expected to continue the market-friendly policies of Lula, though some analysts and political allies say she may also expand the role of the state in key areas of the economy.
The Sensus poll surveyed 2,000 people from Sept. 10-12, and has a margin of error of plus or minus 2.2 percentage points. (Writing by Stuart Grudgings; Editing by Todd Benson and Vicki Allen)
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