(Adds Bolsonaro appeal to voters)
By Anthony Boadle
BRASILIA, Oct 5 (Reuters) - Far-right front-runner Jair Bolsonaro appealed to Brazilians on Friday to turn out to vote for him on Sunday and give him an outright victory to avoid a run-off that some polls say he could lose to a leftist challenger.
Brazil's most polarized election since the end of military rule in 1985 pits Bolsonaro, a former Army captain running on a law-and-order platform, against leftist Fernando Haddad of the Workers Party, whose leader is in jail for corruption.
Bolsonaro said he was 6 million votes short of winning the election on Sunday by a majority. If a run-off was necessary, it would be held on Oct. 28 between the two leading candidates.
"Let's avoid a second round," he appealed to supporters in a live Facebook feed, asking them to convince relatives and friends to vote for him.
An Ibope opinion poll on Wednesday had Bolsonaro nine points ahead of Haddad, but showed that he could lose a run-off. Final polls on Saturday will determine if a second vote will be needed.
Bolsonaro said an outright win on Sunday would give him a strong mandate to take office without having to enter the traditional horse-trading with political parties needed by Brazilian presidents to form coalition government.
About 26 percent of voters say they have yet to decide who they will vote for, according to the most recent poll released on Thursday by Datafolha, which showed that outright victory by Bolsonaro was still possible but not likely.
Bolsonaro, who is recovering from a near-fatal knife attack while he was campaigning, skipped the last presidential debate of the campaign on Thursday night on Brazil's largest broadcaster TV Globo.
He said he was under doctors' orders to stay away from the debate, but he gave an interview that aired on a rival network on Thursday night.
His decision was emblematic of his unconventional presidential bid that has eschewed traditional campaigning in favor of grassroots organizing through social media and selective interviews.
Bolsonaro has tapped into disillusionment with a weak economy, political graft and rising violence.
A Thursday survey from pollster Datafolha found Bolsonaro had 35 percent support, a jump of 3 percentage points since Tuesday. Haddad stood at 22 percent.
In the TV interview, Bolsonaro slammed Haddad for being a "puppet" of jailed former president Luiz Inacio Lula da Silva.
Haddad, a former mayor of Sao Paulo, was confirmed at the top of the Workers Party ticket three weeks ago, replacing Lula, who was barred from running due to a corruption conviction. He has called Lula a key adviser, but has denied any plans to pardon the former president or give him a role in government.
Bolsonaro has faced federal charges of hate speech after racist, homophobic and misogynist rants, but in a live speech on Facebook earlier on Thursday he rejected the accusations.
In recent weeks, as Bolsonaro's poll numbers have risen, his rivals have found it hard to draw attention from the convalescing former army captain. His vows to loosen gun laws and declare war on drug gangs have thrilled his supporters and terrified his critics.
An admirer of Brazil's 1964-1985 military dictatorship, Bolsonaro has won massive support from the fast-growing evangelical community by vowing to block the legalization of abortion, gay marriage and drugs.
Brazilian markets have rallied on the prospect of Bolsonaro stopping a return to power by the Workers Party. Investors blame the party for plunging Brazil into its worst recession in 2015-2016.
Brazil's real currency was up more than 0.5 percent against the dollar on Friday, while the Bovespa stock index rose 0.3 percent.
Bolsonaro's economic positions remained unclear. Last week he asked his economic adviser, Paulo Guedes, and his running mate, retired General Hamilton Mourão, to hold off on making public statements after contradictions emerged over economic policy.
In an interview published on Friday by newspaper Estado de Sao Paulo, one of the candidate's top economic advisers said Bolsonaro would push ahead with privatizing state power firm Centrais Eletricas Brasileiras SA, or Eletrobras.
However, he pledged to keep state oil company Petroleo Brasileiro SA, known as Petrobras, and lender Banco do Brasil SA in government hands.
"Everything that is strategic will be maintained, such as oil and gas fields," former army General Oswaldo de Jesus Ferreira told the newspaper. Ferreira is one of many military men with key roles on Bolsonaro's team.
The comments by Ferreira, who said he was in the same military graduating class as his "brother" Mourão, tempered promises of Wall Street-favorite Guedes, who told Reuters in May that Brazil should privatize everything from Petrobras to state banks in order to cut debt and fund local governments.
Reporting by Anthony Boadle Additional reporting by Gabriel Stargardter Editing by Brad Haynes, Clarence Fernandez, Jeffrey Benkoe, Toni Reinhold