* Centre-left leads in vote for mayor of Rome
* Grillo's 5-Star Movement suffers setback
* Local elections could complicate relations in coalition
Italian Prime Minister Enrico Letta hopes to lift his bruised centre-left party in local elections that conclude on Monday, strengthening his hold over an uneasy coalition government with its traditional rivals on the centre-right.
The votes in Rome and other cities will have no direct effect on the national government but will test the fragile partnership between Letta's centre-left Democratic Party (PD) and the centre-right People of Freedom (PDL) party of former premier Silvio Berlusconi.
It may also heighten problems for the anti-establishment 5-Star Movement of comic Beppe Grillo, which has been shaken by growing unhappiness about his authoritarian style and which saw its support fall sharply in a first round of voting last month.
The vote in Rome, where centre-left challenger Ignazio Marino took a strong lead over centre-right mayor Gianni Alemanno in the first round, has been seen as a boost for Letta as he seeks to impose his authority on his unlikely coalition.
Letta has had to reconcile competing demands for tax cuts and job-creating measures to pull Italy's economy out of nearly two years of recession with pledges to shore up battered public finances and cut state debt.
He has rejected suggestions that a deadlocked national election in February, which forced the two main parties into an unwilling coalition, had effectively left Berlusconi as the "driver" of the government.
"The result of the local elections will show that it isn't like that," he said at a conference in Florence on Saturday and insisted there was no alternative to the coalition.
However Berlusconi, who faces two verdicts this month on an appeal against a tax fraud conviction and a separate trial on charges of paying for sex with a minor, remains an unpredictable ally.
He has demanded the government scrap an unpopular housing tax, despite the hole that would create in Italy's already strained public finances, and has called for Letta to change course in Europe and seek a "trial of strength" with German Chancellor Angela Merkel to loosen budget constraints.
Some 6 million Italians are eligible to vote in Rome and smaller cities including Siena, Ancona, Brescia and Viterbo and in separate polls in the Sicilian towns of Messina, Catania, Siracusa and Ragusa.
Voting began on Sunday morning and will close on Monday at 1300 GMT, with results expected by the evening.
The PD is hoping it can regain the initiative after nearly imploding in the wake of the February election, when it threw away a strong opinion poll lead before the vote, but speculation of an imminent collapse of the government has faded.
"There are a lot of hidden mines and bombs put under the table and also objective problems, but at the moment things are going forward," Renato Brunetta, the PDL's parliamentary leader in the lower house, told Reuters last week.
"There are no guarantees but as long as the government keeps governing, it will continue," he said.
However the mood among voters remains volatile, with unusually high rates of abstention in first-round votes in some cities underlining the deep disillusion many Italians feel with their political leaders.
Even Grillo, whose rebel movement captured a quarter of the vote in the February election, has felt the backlash, with the results of the first-round voting in Rome showing his candidate's share of the vote had halved.
He has railed against the coalition, which he described as the product of a "permanent coup d'etat" but also blamed voters for supporting parties which he said were responsible for Italy's long decline.
The vote in Sicily will be a particular test for his movement after the stunning success it registered in local elections in a number of Sicilian cities in October last year, which set the scene for its triumph in February.