ASUNCION, April 18 (Reuters) - Paraguay's presidential front-runner on Friday rejected the idea that Sunday's election could turn violent, even amid concerns about fraud.

A former Roman Catholic bishop who left the priesthood to head a center-left coalition, Fernando Lugo leads polls with between 30 percent and 40 percent of voter support.

He is in a close race with ruling Colorado Party candidate Blanca Ovelar -- the first woman to run for president of Paraguay -- and retired army Gen. Lino Oviedo of the rightist UNACE party.

"I don't believe in this possible violent scenario," Lugo told foreign correspondents at his campaign headquarters. "All of our elections have been peaceful, regardless of the results."

Lugo aims to end the 61-year rule of the Colorado Party, which is the world's longest-serving political group still in power. The Colorado Party backed Gen. Alfredo Stroessner's 35-year dictatorship in the poor, landlocked South American country until helping to oust him in 1989.

"Many people see a change in Paraguay's political scene after 60 years as something apocalyptic. But our alliance wants to affirm that this will be a genuine, transparent transition ... peaceful, open to dialogue, serene and mature," Lugo said.

Outgoing President Nicanor Duarte Frutos has said Venezuelan and Ecuadorean "agitators" backing Lugo planned to take up arms if their candidate lost.

At the same time, many ordinary Paraguayans fear the Colorado Party could buy votes or bribe election officials to remain in power.

Regarding the possibility of fraud, Lugo said: "There are doubts and distrust ... . This is an issue that is on the front pages and is hanging in the atmosphere."

Sunday's presidential election will be decided by a simple majority, with no second round of balloting. (Reporting by Hilary Burke; Editing by Xavier Briand)

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