* Grillo Movement draws hundreds of thousands to final campaign rally
* Polls suggest 5-Star Movement is Italy's third largest political force
* Momentum fuelled by rage at corruption, scandal
ROME, Feb 22 (Reuters) - Comic Beppe Grillo rounded off the Italian election campaign with a fiery rally in central Rome that drew hundreds of thousands of supporters and underlined the capacity of his 5-Star Movement to create an upset when voting opens on Sunday.
Arriving in his distinctive campaign bus, Grillo launched into his now familiar tirade against corrupt politicians and bankers, taking aim against targets ranging from Silvio Berlusconi and Mario Monti to German Chancellor Angela Merkel.
"Give up! You're surrounded!" he bellowed to cheers from the crowd estimated by stewards at more than half a million, many of whom had waited for hours in the rain before his arrival at Piazza San Giovanni, a traditional meeting place of the left.
The rally was the last stop on Grillo's "Tsunami Tour" which has taken the shaggy-haired 64-year-old across Italy in a camper van, yelling himself hoarse at packed meetings complemented by the most effective Internet campaign in Italian politics.
It contrasted sharply with the much quieter final campaign appearances of rivals including Berlusconi, who was prevented from being present at the last rally of his centre-right party because of what he said was an eye problem.
Tapping into the pent-up rage that millions of Italians feel over the corruption and privilege of their political elites, Grillo has built his 5-Star Movement from a fringe phenomenon into one of the most talked-about electoral forces in Europe.
Manuela Rossetti, 30, a doctoral student in archaeology, left Italy for France along with many of her friends because she saw no future in her own country, where the economy has barely grown in a decade.
"The politicians are an elite; they are not part of Italian society any more and they don't understand the problems of ordinary people," she said as she waited for Grillo to arrive.
On a brief return home, she will be voting in the election on Sunday and Monday.
"The 5-Star Movement winning the elections is my only hope this country can change, and maybe I can return," she said.
The last opinion polls before a pre-election blackout two weeks ago gave Grillo's movement some 16 percent of the vote, making it the third-largest electoral force. However, several electoral experts believe that it may have built on that score, helped by a string of corporate and political scandals.
Although Grillo himself is not running for a seat - a felony conviction over a road accident in the 1980s means he is barred under his own rules - the movement is on course to send scores of novice deputies to parliament, where they could have a significant impact on the make-up of the next government.
Attacked by mainstream politicians as a dangerous populist and a threat to democracy in a country that lived through two decades of fascism until World War Two, Grillo has ruled out an alliance with any of the big parties and constitutes one of the biggest elements of uncertainty in the election.
He wants a referendum on retaining the euro currency, to restructure Italy's huge public debt and strip politicians of their privileges but the rest of his platform is an eclectic mix ranging from free health care to protecting local manufacturing.
With record unemployment and a recession worsened by the austerity policies imposed by technocrat Prime Minister Mario Monti to stem the debt crisis, the mood among many Italians is bleak.
"In Italy there are business owners committing suicide. There are people without enough to eat," said Armando Mattioli, 61, a doctor who travelled by bus from the central city of Perugia to attend Grillo's rally. "We are in an emergency."
Investigations into alleged fraud and corruption at companies including defence group Finmeccanica and Italy's third largest bank, Monte dei Paschi, plus a seemingly endless round of political corruption cases have fuelled the movement.
But Grillo's often spiky relations with the mainstream media were again in evidence on Friday after organisers banned Italian journalists from the backstage area, admitting only the foreign media until police ordered them to let in local reporters.