ROME (Reuters) - The mayor of Rome, elected in June in a breakthrough for the anti-establishment 5-Star Movement, suffered a major setback on Thursday when key members of her city government resigned along with the chiefs of the municipal transport and refuse companies.


Virginia Raggi's performance as mayor is widely seen as critical to the prospects of 5-Star, which polls suggest has a strong chance of victory the next national election, due in 2018.


She won the June 19 election with a crushing 67 percent of the vote against the candidate of Prime Minister Matteo Renzi, promising to turn around a city beset for years by corruption and poor public services.


5-Star's leaders believe success in Rome can be a stepping stone to national government, but Raggi's early months in office have been hard.


After internal party bickering delayed the formation of her city government, she seemed to have finally made progress in overcoming Rome's chronic problems with trash collection before Thursday's shock resignations.


The councilor responsible for fixing Rome's debt-ridden budget quit along with Raggi's chief of staff, followed by the director general and the CEO of the city's transport company ATAC and the head of its trash collection firm AMA.

Raggi's chief of staff has been at the center of a controversy over her high salary, while the head of the city's budget policy, Marcello Minenna, did not say why he was leaving.

The chief of AMA said he could not continue without Minenna, who had chosen him, and the director general of ATAC said city hall had meddled in personnel issues and he had not received funds promised to turn the company around.

Politicians from Renzi's Democratic Party said the chaos proved that 5-Star was unfit to govern, while Paola Taverna, a lower house deputy and one of 5-Star's most prominent figures, admitted the resignations were "a heavy blow".

The 5-Star Movement is running neck-and-neck with the PD, according to opinion polls, but the same polls suggest that it would be most likely to emerge victorious under Italy's two-round voting system.

(Reporting by Massimiliano Di Giorgio Writing by Gavin Jones; Editing by Alison Williams)