Trudging into Paris with blistered feet after a 10-day march from a steel mill in northeast France at risk of closure, steelworker Jerome Baroin was in no mood to discuss President Nicolas Sarkozy's re-election bid.

Sarkozy has done nothing for us. His promises were just lies, said Baroin, 29, whose 350 kilometre (220-mile) march with 17 other workers from the idle plant in Florange, by the German border, highlights an embarrassment for the conservative incumbent.

The steelworkers have a specific gripe: two weeks into his campaign, Sarkozy said he had clinched a deal with owner ArcelorMittal to restart the furnaces, but the company later said it would only do so once the economy recovered.

More broadly, polls show he is failing to reconquer blue-collar workers, the swing voters who helped him to power in 2007, swept up by his work more to earn more slogan. Now they could sink his hopes of a second term next month as they drift, disenchanted, to the left.

While 52 percent of workers picked Sarkozy in the 2007 run-off and 48 percent voted Socialist, polls show 60 percent could back Socialist Francois Hollande and just 40 percent Sarkozy.

Blue-collar workers and retirees make up a fifth of the electorate and switch political allegiances more than other social groups, perhaps because their low incomes make them more receptive to campaign promises, pollsters say.

Sarkozy and Hollande sparked off their battle for the working class vote early in the campaign for the two-round election on April 22 and May 6, criss-crossing France to tour factories and vowing to save industries and jobs.

With 350,000 industrial jobs lost during Sarkozy's term, the president has often been met with crossed arms and stony glares. Hollande, who is happy to don a hard hat or stand on a union van to speak, does only a little better.

Two weeks before the first ballot, polls show workers are disillusioned with the president and barely warmer to his bland Socialist rival.

The far right still draws the most working-class voters, but a growing trickle are now abandoning the National Front's Marine Le Pen for hard left candidate Jean-Luc Melenchon, a firebrand orator not afraid to raise his left fist in salute.

That is another blow for Sarkozy. He can count on many far-right voters to rally behind him in a run-off against Hollande, but Melenchon's popularity across social classes could well help secure an Hollande victory, as polls show 80 percent of the radical's supporters will switch to the Socialist in round two.

While workers' first-round voting intentions have settled at 20 and 22 percent, respectively, for Sarkozy and Hollande in surveys by pollster BVA, their support for Melenchon has leapt to 16 percent from 7 percent in January.

Blue-collar workers are the biggest electoral group, and they have abandoned Sarkozy en masse, said Guy Michelat, an academic at Sciences Po university who studies the worker vote.

They were the ones Sarkozy made big promises to in 2007, so they're more disappointed with him than the middle class.

WORKERS A KEY TARGET

Melenchon is backed by the remnants of the once-mighty Communist Party, which polled more than 20 percent in the 1970s but less than 2 percent at the last presidential election.

In a far-left revival, he is pulling workers out of abstention and stealing votes from Le Pen, whose blue-collar support has slipped 5 points to 25 percent in the BVA polls.

The historic aura of the working class gives it symbolic importance, but its sheer size and the fact that workers are more likely to change the way they vote means it also has a real electoral importance, said Gilles Finchelstein, head of the Fondation Jean Jaures think-tank, close to the Socialists.

Over the past month we've seen a strong rise in support for Melenchon among workers, Finchelstein said, adding that he gave voice to their discontent.

The worker surveys make grim reading for Sarkozy, who five years ago promised an economic revolution that would put more money in the pockets of hard workers, winning over a slice of France that had been wedded to the left for decades.

He created tax breaks for overtime work in an effort to unpick the 35-hour week instituted by the Socialists in 2000.

For most of the 20th century, three-quarters of France's blue-collar workers voted Communist. Marxist influence on the education system ensures an enduring sympathy for organised labour, and politicians of all stripes find a receptive audience nowadays when bashing globalisation as a threat to French jobs.

Disillusionment with Socialist economic management, high unemployment and hostility to immigration drove growing numbers of industrial workers to back National Front founder Jean-Marie Le Pen from the 1980s.

His daughter Marine, who wants jobs and welfare benefits reserved for French workers over immigrants, is still popular on the factory floor.

LOST TRUST

Polls show workers are punishing Sarkozy for failing to bring down unemployment or improve their living standards during a term scarred by economic crisis. Low-income voters see him as a president of the rich who eased taxes on the wealthy.

Sarkozy's 2007 message resonated with blue-collar workers, as income is their top concern, but he has lost his credibility on purchasing power and employment, said Eric Bonnet, head of political studies at pollster BVA. His popularity is especially low among workers. They don't trust him at all.

Both mainstream candidates put the fight against industrial decline at the heart of their campaign, with Sarkozy vowing to lower labour costs and Hollande vowing investment in innovation.

Neither seems to have convinced their target audience. Workers at plants suffering closures and redundancies say they are tired of empty promises and political ideology.

We've been betrayed for 40 years now. We have no more time for speeches and promises, said Edouard Martin, a CFDT union offical leading the Florange workers, who were tear-gased by police last month when they sought a meeting with Sarkozy.

Melenchon has pricked up ears on factory floors with his promises to raise the minimum wage to 1,700 euros a month from 1,400 and ban profitable firms from laying off workers.

By late February, a survey by TNS-Sofres found 35 percent of respondents thought Melenchon would defend workers best, giving Hollande 30 percent, Sarkozy 12 percent and Le Pen 10 percent.

Melenchon speaks the language of the traditional left and sounds like he understands people's problems, said Michelat.

He has given a sense of existence back to the working class, who find Hollande a bit wet.

(Reporting By Catherine Bremer; Editing by Paul Taylor)