French President Nicolas Sarkozy was set to formally declare his candidacy for a second term on television on Wednesday, hoping to overcome deep unpopularity with a short and intense campaign.

The centre-right president, who lags Socialist challenger Francois Hollande in all opinion polls, launched his Twitter feed with the news that he had accepted an invitation to appear on TF1's evening news at 7 p.m. British time.

With the long-expected announcement, Sarkozy will formally enter the race, although opponents say he has been campaigning stealthily for months.

Now the real campaign starts, Foreign Minister Alain Juppe, a close Sarkozy ally, told France Info radio.

Despite polls showing Hollande would beat Sarkozy by up to 15 points in a May 6 runoff between the two, the president's camp is confident he can narrow the gap before the April 22 first round.

Despite a disapproval rating of 68 percent, Sarkozy hopes to present himself as an experienced leader who can drag France out of the economic slump and overcome the euro zone crisis alongside German Chancellor Angela Merkel.

But with unemployment stuck at a 12-year high of 9.3 percent and a stream of news about companies closing or relocating production abroad, Sarkozy -- who took office in 2007 pledging a return to full employment -- faces an uphill struggle.

Credit rating agency Moody's warned on Monday that it could follow Standard & Poor's and remove France's AAA rating. Finance Minister Francois Baroin has promised to stick to measures designed to promote growth and cut France's deficit.

GDP data on Wednesday provided a rare glimmer of hope.

Preliminary data from the INSEE statistics office showed that French gross domestic product (GDP) eked out 0.2 percent growth in the fourth quarter. A Reuters poll of 36 economists had predicted on average a 0.1 percent contraction.

It was the first time since the beginning of 2009 that French quarterly growth outperformed neighbouring Germany, which Sarkozy has repeatedly held up as the economic model to follow.

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In the past weeks, Sarkozy has announced a VAT sales tax increase to fund a cut in payroll charges and is introducing a 0.1 percent tax on financial transactions.

He is expected to flesh out his campaign platform in a keynote speech in the Mediterranean port city of Marseille on Sunday. A formidable campaigner, Sarkzoy plans to hold his first rally on Thursday in the Alpine town of Annecy.

Socialist Party leader Martine Aubry described Sarkozy entering the campaign as a non-event.

The French aren't interested in this sort of communication ... they want us to deal with their problems, she said on French television station LCI.

Sarkozy's announcement coincides with Hollande's second major campaign speech on Wednesday in his home city of Rouen.

A Harris Interactive poll of first-round voting intentions, published on Wednesday, showed Hollande and Sarkozy each gaining one point at 28 and 24 percent respectively.

Far-right leader Marine Le Pen was seen winning 20 percent, centrist Francois Bayrou 13 percent and far-left challenger Jean-Luc Melenchon eight percent. In the run-off second round on May 6, Hollande would beat Sarkozy 57 percent to 43 percent.

Polling analysts say that with just nine weeks to go, Sarkozy will have a hard time to make up so much lost ground.

We have rarely seen a president so far behind the challenger at this point in the campaign, Harris Interactive polling chief Jean-Daniel Lévy told Reuters.

Sarkozy still has a small change of winning if he manages to pull the Socialist candidate into his issues of immigration and security, and as long as the debate does not focus on his personality or achievements, Lévy added.

Sarkozy and Hollande both say their priority is to restore public finances and whoever becomes the next president will have to push through roughly 100 bilion euros of austerity measures in the next five years to plug the state deficit.

But they propose very different ways to reach that goal.

Hollande kicked off his campaign in late January with an economic programme that would raise taxes on banks, big firms and the wealthy to help him reduce the public deficit while pumping more funds into education and state-aided job creation.

Juppe, once seen as a possible alternative conservative candidate, said that nothing was lost for Sarkozy.

We have seen this kind of situation before and it is now that the campaign starts, it is now that the president as a candidate will outline his priorities and that we will see the weaknesses of the Socialist candidate, he said.

(Reporting by Marine Pennetier, John Irish and Geert De Clercq; Writing by Geert De Clercq; Editing by Paul Taylor)