By Anthony Boadle
BRASILIA (Reuters) - President Dilma Rousseff has a clear lead over opposition candidate Aecio Neves and would win Sunday's presidential election runoff by six to eight percentage points, two opinion polls showed on Thursday.
In Brazil's tightest election in decades, the leftist incumbent's aggressive campaign against pro-business senator Neves has succeeded in bolstering her support while increasing rejection of her rival, the surveys showed.
Rousseff has gained ground by reminding voters of the rising wages and expanding social programs many have enjoyed over the past 12 years of Workers' Party rule, benefits she said would be at risk because Neves would govern for the elite.
The new surveys were the first by Brazil's major polling firms Ibope and Datafolha to show Rousseff with a lead greater than the margin of error, which is plus or minus 2 percentage points for both.
Rousseff has 49 percent of voter support against 41 percent for Neves, according to Ibope, and 48 percent versus 42 percent for Neves, according to Datafolha.
Excluding undecided voters, spoiled and blank survey responses, Rousseff would win the runoff by 54 percent of the valid votes against 46 percent for Neves, Ibope said. Datafolha shows her winning by 53 percent versus 47 percent.
"We are seeing a turnaround. It's visible on the streets," Rousseff, 66, who was trailing Neves last week, said at a news conference at a Rio de Janeiro hotel where she was preparing for Friday night's final television debate.
An undaunted Neves dismissed the polls as unreliable, saying they had failed to detect his surge in the Oct. 5 first round vote in which he unexpectedly placed second ahead of popular environmentalist Marina Silva.
Neves, 54, told reporters in Rio that Rousseff had run a "sordid" campaign that was a full of lies about him.
His attacks on Rousseff - he called her a "liar" and "flighty" in an acrimonious debate last week - have lost him support among women voters who perceived his comments as male chauvinist. Rousseff has overtaken Neves among women voters by a margin of 6 percentage points.
The number of Brazilians who say they would never vote for Neves has increased 7 percentage points since last week, to 42 percent, Ibope said.
Rousseff's rejection rate has remained unchanged, while the approval rating of her government has climbed to 44 percent from 42 percent earlier this week, Datafolha said.
Neves, the market favorite, insists he would preserve social programs while curbing other government spending, taming inflation and ending what he calls heavy-handed industrial policies in order to restore investor confidence in a economy that slipped into recession in the first half of the year.
But his promise of economic recovery appears to have lost weight among many Brazilian voters who are increasingly optimistic about Brazil's economy, according to a Datafolha poll released on Wednesday.
Rousseff has gained momentum in the last two weeks mainly among Brazil's lower-middle class, which has gained access to modern consumer goods and education under the Worker's Party and does not appear to have been swayed by Neves.
(Additional reporting by Felipe Pontes and Rodrigo Viga Gaier in Rio de Janeiro; Editing by James Dalgleish, Grant McCool and Dan Grebler)