Radical leftist Jean-Luc Melenchon drew another huge crowd to a political rally on Saturday, this time at a beach in Marseille, riding a wave of support that could help secure a Socialist victory in an April-May presidential election.

Melenchon, who briefly surged into third place in the polls behind Socialist Francois Hollande and conservative Nicolas Sarkozy last week ahead of the April 22 first round vote, told flag-waving supporters they were making history and that their anti-capitalist fight would continue after the election.

Officials for Melenchon's Left Front grouping of far-left parties said 120,000 people attended, matching the crowd Melenchon drew to the Bastille in Paris a month ago. Witnesses put the number at closer to 80,000 people.

The fight is the fight and I ask you to remember that with the Left Front you don't just have a voting slip but you have a team of men and women who are organising a fight for the long term which will not end on the date others might think, because that's when it will all start, Melenchon told the crowd.

We must end the right's power for good. Whatever happens, we must beat them, he roared.

While the far-leftist, who wants a citizens' revolution to curb the power of free markets, stands little chance of making it into a May 6 presidential runoff, his soaring popularity is a headache for Hollande as he could win a bloc of parliamentary seats in June elections and demand a government post.

Melenchon says he will focus on a street-led push for a higher minimum wage and caps on salaries, as well as higher taxation of the rich, hinting at mass protests. However, he has said he is opposed to disruptive strike action.

The former Trotskyist also wants to pull France out of European budget stability pacts, including the recent fiscal compact credited with calming financial markets over the euro zone's debt crisis.

Saturday's crowd, framed by sunlit mountains and the Mediterranean sea, filled the Prado public beach which city officials gave the Left Front permission to use after they threatened to otherwise march through Marseille.

The force is there and its immense. We'll show them we are bigger than they are, Melenchon told reporters at his campaign headquarters on Friday, noting that 4.7 million viewers watched him on a TV debate this week, more than those who watched Hollande or Sarkozy.

The firebrand orator is the star of the fringe candidates in part due to his combative charisma and in part due to a deep-rooted anger over three years of economic malaise and rampant unemployment that the public blames on financial markets.

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Melenchon's manifesto promises to raise the minimum wage to 1,700 euros ($2,200) a month from 1,400 euros, to confiscate any income above 360,000 euros a year, to reinstate retirement at age 60 for all, and to ban profitable companies from laying off workers.

He reiterated his loathing for unfettered markets on Saturday, making it clear he is taking the opposite tack to Hollande, who told Reuters during a trip to London earlier this year that he was not dangerous.

We are not sheep. We will fight back. I have the addresses of these bankers, he said, adding partly in English: If you feel 'very dangerous', welcome to my club.

Melenchon jested that Hollande and Sarkozy had been driven to hold big open-air rallies planned for Sunday in Paris because they feared the big crowds he was drawing, made up of blue-collar workers to middle-class left-wing idealists.

We have created a new fashion and it's so powerful that they have all decided to come out and hold open-air meetings to try and do as well as us. We are happy to see them come out and get some fresh air, he quipped.

While Hollande stands to gain from Melenchon's popularity, as polls show 80 percent of far-left voters will back the mainstream Socialist on May 6, financial analysts are nervous that a strong far-left parliamentary bloc could tie Hollande's hands.

In the latest voter surveys Melenchon has dropped back into fourth place but he is still forecast to win 13-17 percent support in the first round vote. He plans another outdoor rally in the north of Paris on April 19, three days before the vote.

(Writing by Catherine Bremer; Editing by Andrew Osborn)