By Deepa Babington
ROME (Reuters) - Italians begin voting on Sunday in local election run-offs where Prime Minister Silvio Berlusconi's center-right coalition risks humiliating defeat in his home town of Milan for the first time in nearly 20 years.
Nearly 6 million voters are eligible to cast their ballots in contests in 90 towns and six provinces, but the focus is squarely on the key battlegrounds of the financial capital Milan and the southern port of Naples.
Berlusconi took a drubbing in the first round of voting on May 15 and 16, when an uninspired center left managed to hold on to power easily in Turin and Bologna and forced the center right into run-offs in Naples and Milan, its northern power base.
The media magnate had cast the vote as a referendum on his popularity and policies, and was punished by voters for a series of sex scandals, corruption cases and a stagnant economy. Days later, ratings agency Standard & Poor's lowered its outlook on Italy for failing to reduce its public debt and boost growth.
Defeat in the run-offs, especially in Milan, would be a serious blow for Berlusconi, deepening divisions in the center right and potentially provoking challenges to his leadership.
"The Berlusconi era is ending," Walter Veltroni, a former center-left leader whom Berlusconi defeated in national elections in 2008, told the left-wing newspaper L'Unita on Saturday.
"This administrative vote has made it clear that there is a crisis in the center right and a profound split in opinion among a public that is tired of being taken for a ride."
Initially stunned into silence by the first-round results, Berlusconi has since taken to the campaign trail with a vengeance. Blanketing the airwaves with tirades against his long-time enemies, the left and magistrates, he has predicted Milan will become an "Islamic gypsyland" if the left wins and accused leftist voters of lacking a brain.
He wrapped up campaigning on Friday with a trademark burst of energy and defiance. Hours after the Group of Eight summit in Deauville, France, where he complained to U.S. President Barack Obama about a "dictatorship of leftist judges" in Italy, Berlusconi flew to Naples for a flurry of television interviews and a duet with a Neapolitan singer at a campaign rally.
Asked if the center right would face a crisis in the event of defeat, Berlusconi said: "I categorically exclude that."
A general atmosphere of acrimony marked the end of campaigning on Friday, with a fire sweeping through an election office for the center-right candidate in Naples and two people hurt in a brawl between supporters of rival candidates in Milan.
In Milan, leftist Giuliano Pisapia is looking to unseat center-right mayor Letizia Moratti, who received just 41.6 percent of the first-round vote against her rival's 48 percent.
In Naples, a divided center left which fielded two candidates in the first round could fare better with a unified front in the run-offs, although both sides have taken flak for failing to resolve a chronic garbage crisis plaguing the city.
(Editing by Louise Ireland)