By Steve Scherer
ROME (Reuters) - Beppe Grillo, the irreverent comic who co-founded Italy's anti-establishment 5-Star Movement, declared he was taking back leadership of the bloc this weekend ahead of a year-end referendum that could sink the government.
Saying he was "tired", Grillo stepped aside two years ago, letting a five-member directorate take care of the movement's day-to-day decision making, backed by 5-Star strategist and co-founder Gianroberto Casaleggio.
But much has changed since then. Casaleggio died in April, and missteps by Virginia Raggi, the 5-Star mayor of Rome elected earlier this year, have exposed rifts and confusion among the movement's top lawmakers.
"I'm back," Grillo announced to the 5-Star faithful, tens of thousands of whom filled a large square in the Sicilian capital of Palermo late on Saturday for the movement's annual meeting, which continues on Sunday.
"I will be the political boss and I will take decisions because someone has to," he said during a speech broadcast on TV. Earlier, before taking the stage, Grillo said he would take charge at least until the elections.
Wearing blue jeans and a cotton shirt with the sleeves rolled up, Grillo appeared to relish returning to his role as chief rabble rouser, shouting that the movement had entered its "second phase".
The 5-Star Movement stormed onto the national political scene in 2013 when it won more than 25 percent of the national vote, coming in a close second to the ruling Democratic Party (PD).
With PD Prime Minister Renzi facing a crucial referendum vote on his trademark constitutional reform by the end of the year, the timing of Grillo's announcement appears meant reinvigorate the movement to defeat the referendum and make ready for a vote that could come as early as 2017.
The 5-Star opposes the referendum, which is aimed at streamlining lawmaking and seating stable governments, saying it would concentrate too much power in the hands of the government.
But Grillo's announcement runs contrary to a founding principle of the movement: no leaders.
In fact until now the white-maned Grillo, 68, has defined himself as the 5-Star spokesman, not its leader, and has always refused to stand himself for prime minister.
ROME AND REFERENDUM
Grillo's move to take the reigns of what has become one of Europe's most potent anti-establishment movements -- it wants a national referendum to decide whether Italy should abandon the euro -- follows a disastrous month for Rome's 5-Star mayor.
Since winning a landslide victory in June, Raggi has been beset by resignations, infighting and scandals. Her election to the high-profile post had been meant to show the movement was ready to govern.
But it is Prime Minister Renzi who is facing an even bigger challenge. On Monday Renzi's government is due to announce the date of the referendum, which will be held either at the end of November or the beginning of December.
Polls show that the outcome of the vote is still too close to call, but the momentum seems to be building against the constitutional overhaul. If Renzi losses the vote, the future of his government will be highly uncertain.
Italy is due to hold an election in the spring of 2018, but it could come sooner if President Sergio Mattarella were to fail to find a temporary solution, and some recent polls show the 5-Star Movement is the country's most popular party.
(Reporting by Steve Scherer,; Editing by Clelia Oziel)