Nicolas Sarkozy is set to formally enter France's 2012 presidential race on Wednesday, kicking off a rapid-fire re-election campaign with the odds stacked in favour of Socialist challenger Francois Hollande.

The conservative leader is expected to declare his candidacy on prime time television on Wednesday evening and hold his first campaign rally on Thursday in the Alpine town of Annecy, where his ruling UMP party expects a deluge of supporters.

Sarkozy is set to flesh out his campaign platform in a keynote speech to an audience of several thousand in the Mediterranean port city of Marseille on Sunday.

Sarkozy's office would not comment on the timing of the launch, but TF1 television has the president as a provisional guest on its 8 p.m. (1900 GMT) news show and Le Figaro daily, which backs Sarkozy, said he would make the announcement then.

Stuck with a 68 percent disapproval rating and trailing Hollande in opinion polls, Sarkozy has been working for weeks on a campaign based around reforms to boost flagging industrial competitiveness and restore growth that has petered out to zero.

An Ifop poll published on Tuesday gave Hollande a 5-point lead in the April 22 first round with 30 percent support to Sarkozy's 25 percent. It showed him easily defeating Sarkozy in a May 6 runoff with 57.5 percent to 42.5 percent.

The survey gave far-right leader Marine Le Pen 17.5 percent in the first round and centrist Francois Bayrou 12.5 percent.

Sarkozy, a barnstorming campaigner, is expected to sound remorse for pledges derailed by the 2008 economic crisis but try to paint himself as an experienced helmsman who can lead France out of the latest round of economic turmoil.

He has also indicated he will take a firmly conservative line on immigration and values issues, opposing as gay marriage and euthanasia.

Hollande will be giving his second major campaign speech on Wednesday evening address to some 7,000 people in his home city of Rouen when Sarkozy makes his announcement.

The Socialist candidate played down the timing, saying the president had been in full campaign mode for several weeks.

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.

Sarkozy has opted to wait until closer to a March 16 deadline to use the benefits of incumbency. But has been on the warpath since a New Year address to the nation, in which he laid the way for a rash of measures to cut labour costs and shift the tax burden to consumption, aimed at reigniting economic growth.

The Socialist Party complained to France's election watchdog on Monday that Sarkozy had used taxpayer money to pay for official trips that were thinly veiled election campaign stops.

(For a graphic of French election opinion polls, click on http://r.reuters.com/was36s)

(Reporting by Catherine Bremer; Additional reporting by Catherine Lagrange in Lyon; Editing by Paul Taylor)