* 5-Star Movement leader Grillo tested by internal dissent
* Rise in party support has flattened, may be waning
* Primaries to pick election candidates draw criticism
By Gavin Jones
ROME, Dec 12 (Reuters) - Italy's anti-establishment 5-Star Movement, which has enjoyed a meteoric rise in public support over the last year, is suddenly looking more ragged and disunited just as an election campaign gets under way.
Comedian Beppe Grillo, the movement's charismatic founder and chief, on Wednesday expelled two prominent party members after weeks of growing internal dissent towards what critics say is his dictatorial leadership style.
Grillo, who is famous for his rants against Italy's ruling classes, on Tuesday turned his fire on his own party, saying he was fed up with internal sniping and that anyone with complaints against him could "get out of the movement".
"Don't come and break my balls, me of all people, about democracy. I'm getting fed up, I'm getting angry, seriously angry," Grillo wrote on the 5-Star Movement's blog, its main forum for communication.
On Wednesday he again used the blog to expel two prominent critics, Giovanni Favia, a councillor in the regional government of Emilia Romagna, and Federica Salsi of the city government of Bologna, the capital of the same northern region.
The decision sparked a barrage of angry tweets among the party's mostly young, internet-savvy supporters, many comparing Grillo with famous dictators including Benito Mussolini, Nicolae Ceausescu and Joseph Stalin.
Salsi said her expulsion confirmed there was no internal democracy in the movement and she suggested that Grillo's real aim was to make money through the party rather than effect political change in Italy.
The 5-Star Movement, bolstered by public disgust at the waste and corruption among established parties, has seen its support increase from 1.8 percent in 2010 to around 20 percent, making it Italy's second-largest party in opinion polls.
The three-year-old party attracts mainly young, well-educated people tired of established parties and has some city mayors and numerous local government councillors.
However, as campaigning begins for what would be its first national election expected in February, polls suggest its rise has flattened and is now ebbing slightly from that peak.
Media attention is focusing more on the established parties than on the foul-mouthed diatribes of the shaggy-haired, 63-year-old Grillo, who wants to hold a referendum on whether Italy should leave the euro zone.
Support for the centre-left Democrat party jumped to above 30 percent this month following its highly publicised primaries to select its candidate for prime minister.
By contrast the 5-Star Movement's own primaries, held on the Internet last week to elect its candidates for parliament, were widely criticised for a lack of transparency and were estimated to have attracted fewer than 50,000 online voters.
Grillo's decision to shun all television debates with established parties, which has worked well so far, may also come unstuck as the election campaign heats up if millions of undecided Italians turn to such debates to help them make up their minds. (Reporting By Gavin Jones, Edited by Richard Meares)