* Tens of thousands turn out in Rome for 5-Star leader
* EU election is test of legitimacy of PM Renzi
* Pollster says Grillo has momentum
By Steve Scherer
ROME, May 23 (Reuters) - Comic Beppe Grillo drew tens of thousands to a Rome rally on Friday, showing the potential of his anti-establishment 5-Star Movement to surprise in Sunday's European vote as it did in the national election last year.
Prime Minister Matteo Renzi has a lot riding on the European parliament vote, the first nationwide election he has faced since taking power in a party coup in February.
It will test his political legitimacy as head of the right-left governing coalition and ability to meet the challenge posed by Grillo's appeal to an angry electorate disillusioned by recession, unemployment and political corruption.
The election is being closely watched by Italy's European Union partners, nervous of fresh political instability in the eurozone's third-largest economy, which is struggling to emerge from two years of recession and lower its 2-trillion-euro public debt.
Renzi filled about half of another Rome square at a rally on Thursday, prompting Grillo, speaking to a much larger crowd during the final day of campaigning, to quip: "He was in People's Square last night and there were no people."
The 65-year-old Grillo closed out his campaign for the national vote in the same square last year and went on to win more than 25 percent of the vote, 10 percentage points more than polls had suggested only two weeks earlier.
"He's got momentum again this year," said Maurizio Pessato, head of pollster SWG. "He attracts voters because he still insists that everything must change, and most people look around and see the political system is still corrupt and broken."
The last opinion polls before the pre-election blackout showed Renzi's Democratic Party (PD) had a lead of as many as 10 percentage points over 5-Star, with Silvio Berlusconi's Forza Italia further behind.
The fast-talking and charismatic Renzi, at 39 the youngest leader in Italy's history, has cut taxes for 10 million Italians in a bid to stimulate the economy and pledged to fight European Union austerity.
Renzi emphasises the tax cuts - worth about 80 euros per month for low earners - and promises change.
"It's not enough to shout and insult people," Renzi said at a rally on Friday in Prato, Tuscany. "Eighty euros a month isn't just a small handout. It's something real."
The 77-year-old Berlusconi, currently doing community service at an old peoples' home as his sentence for tax fraud, has compared Grillo to Adolf Hitler and other dictators who came to power promising revolution in tough economic times.
At Friday's rally, Grillo supporter Stefania Mugavero disagreed.
"The 5-Star vote is a protest vote, it's a vote against corruption, a vote for revolution, a vote for hope," he said.
Some PD voters are unsure how their party will fare.
"There are too many people around who are easily swayed by the cheap talk," said Carmen Manuzza at Renzi's speech in Rome. "Berlusconi has lost some of his shine, but Grillo, who is even worse, has taken his place and is really persuading people." (Additional reporting by Antonio Denti and Hanna Rantala; editing by Andrew Roche)