Nicolas Sarkozy was on Wednesday to reveal the worst kept secret in French politics by officially launching his re-election campaign, stepping up a gear less than ten weeks from polling day.

The French president has been operating on a de facto campaign schedule of television appearances and regional tours for months now, despite refusing to confirm his candidacy, but is still trailing in the polls.

On Wednesday, buoyed by better than expected economic growth figures, he was to appear on the main evening news show to throw his hat into the ring, hoping to close the gap between him and Socialist rival Francois Hollande.

"It's a turning point. We are entering another world, that of the campaign," said Nathalie Kosciusko-Morizet, Sarkozy's ecology minister, who has been tipped to become his campaign spokeswoman.

"It's more or less an open secret, a confirmation," opposition Socialist leader Martine Aubry retorted, vowing that Hollande's campaign would not be distracted by the Sarkozy media blitz: "It changes nothing."

Opinion polls consistently forecast Sarkozy will be beaten by Hollande in the second-round run-off on May 6, but the president's camp is clinging to the hope that he can rekindle the energy that brought him to office in 2007.

Wednesday's programme ahead of the television appearance combined the most traditional of French campaign events, a visit to a provincial cheese factory, and the most modern, Sarkozy launching a Twitter account.

In his first two messages on the micro-blogging site he confirmed that he was to appear on the private network TF1 in the evening and invited voters to follow his account and watch him on the show.

The French left has not won a presidential election since 1988, but former Socialist leader Hollande -- the former partner of the party's defeated 2007 candidate Segolene Royal -- has a comfortable lead in opinion polls.

The latest survey published Wednesday by Harris Interactive for the news magazine VSD, forecast that Hollande would win the first round with 28 percent to Sarkozy's 24 then sweep the run-off with 57 percent to 43.

In the Harris figures the only other candidate within striking distance of the second round would be far-right National Front leader Marine Le Pen on 20 percent, but most observers now see the campaign becoming a two-horse race.

Former prime minister and Sarkzoy supporter Jean-Pierre Raffarin told France Inter radio the campaign would be "mano a mano" between the leading pair: "Fundamentally, it's as if we have leap-frogged the first round."

Hollande was to hold a major rally in his hometown of Rouen at the same time as Sarkozy's television appearance, and was to continue hammering away at the alleged injustices of Sarkozy's austerity programme and sales tax rise.

The president began his time in office vowing to liberalise the economy, reduce unemployment and increase voters' spending power, but has instead seen France fall prey to the eurozone debt crisis.

He did have some good news on Wednesday: economic growth in the last quarter of last year was confirmed as having been slightly higher than first thought, and thus France is not officially in recession.

But in a newspaper interview last week to set out his campaign themes, Sarkozy signalled that he would campaign on a conservative social platform rather than on the economy.

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