UPDATE 3-Polls show Rousseff would avoid Brazil runoff

* Two polls show first-round Rousseff victory likely

* Further impact of corruption scandals is limited

* Ruling party alerts followers to avoid complacency (Adds Guedes' quotes, detail)

By Raymond Colitt and Natuza Nery

BRASILIA, Sept 29 (Reuters) - Brazil's ruling party candidate Dilma Rousseff still has a good chance of winning Sunday's presidential election in the first round despite recent ethics scandals that have haunted her campaign, opinion polls showed on Wednesday.

The two polls showed Rousseff comfortably above the 50 percent of valid votes she needs to avoid an Oct. 31 runoff against main opposition candidate Jose Serra and to be elected Brazil's first woman president.

The former chief of staff to President Luiz Inacio Lula da Silva fell 3 percentage points in a survey by pollster Sensus to 47.5 percent, but still had 54.7 percent of the valid vote once spoiled and blank ballots are removed.

She had 55 percent of the valid vote in a separate survey by polling firm Ibope, unchanged from its poll last week.

"In all likelihood, Rousseff will win in the first round," Sensus polling director Ricardo Guedes told reporters in the capital Brasilia.

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Serra, a former governor of Sao Paulo state from the centrist PSDB party, failed to take advantage of Rousseff's loss of momentum, losing a percentage point to 27 percent in the Ibope poll and by a similar amount to 25.6 percent in the Sensus survey.

Former environment minister Marina Silva, the Green Party candidate who has little chance of reaching a runoff, has picked up most of the votes in recent polls. She rose nearly 3 percentage points to 11.6 percent in the Sensus survey and by a point to 13 percent in the Ibope poll.

Rousseff, a career civil servant who at 62 is running for elected office for the first time, has ridden Lula's immense popularity and an economic boom in the world's eighth largest economy to a commanding lead in all opinion polls.

The Sensus poll found that just 4 percent of voters disapprove of Lula's government, reflecting Serra's struggle in convincing Brazilians of the need for change.

Rousseff is widely expected to continue Lula's market-friendly policies and has dismissed the need for major structural reforms, which many economists say are needed if Brazil is to maintain its strong growth of recent years.

She rapidly overtook Serra as soon as campaigning started in earnest, but her advantage has eroded slightly after a former aide quit two weeks ago over corruption allegations that have dominated media coverage. Rousseff has denied wrongdoing.

SCANDAL EFFECT FADING?

The 55 percent of the valid vote that Rousseff has translates into 6.3 million votes above the 50-percent threshold, Guedes said. The damaging effect from the scandals is limited and unlikely to wipe out that lead, he added.

"A type of corruption fatigue is setting in," he said, adding that lower-income, less educated voters were resolute in their support because of the Lula government's welfare measures that have helped pull millions out of poverty.

High disapproval rates for Silva and Serra in the Sensus poll showed they had little room to gain, Guedes said.

A separate survey on Tuesday by pollster Datafolha showed Rousseff losing voter support among middle-class voters, increasing the chances that the election could go to a second round on Oct. 31. [ID:nN28158713]

The ruling Workers' Party urged its members on Tuesday to mobilize voters for Rousseff, apparently concerned that complacency over her victory could give Serra a chance of extending the election to a runoff.

"Let's confirm at the ballot box what we feel in the streets, in the factories, in schools and on the Internet: Dilma victorious in the first round of the election," party President Jose Eduardo Dutra wrote in a letter to members.

Both polls released on Wednesday showed Rousseff would easily win a runoff against Serra by a margin of around 20 percentage points.

Rousseff was due to meet with religious leaders in Brasilia on Wednesday to address their concerns over her stance on abortion, which is illegal in most cases in Brazil, home to the world's largest Roman Catholic population.

Rousseff, who is twice divorced and recovered from cancer last year, has said that abortion is a matter of public health and defends the law that abortions can be provided by the state in cases of rape and when the mother's life is at risk.

Ibope interviewed 3,010 people between Sept. 25-27. The margin of error for the survey was 2 percentage points. The Sensus survey polled 2,000 people from Sept. 26-28, and had a margin of error of 2.2 percentage points. (Writing by Stuart Grudgings; editing by Todd Benson and Anthony Boadle)