By Michel Rose and Ingrid Melander
PARIS (Reuters) - Conservative French presidential candidate Francois Fillon appealed to voters on Wednesday via a newspaper column to back his campaign, trying to claw back support after losing his place as frontrunner over accusations of fake jobs for his family.
Fillon has managed to stem a rebellion within his party, partly for lack of a clear "plan B", but plunging popularity ratings show the 62-year-old, who pegged his campaign on an image of integrity, faces an uphill battle to convince voters.
"It's for you and only you to decide," Fillon told voters in his letter, adding: "Nothing will divert me from the real aim of my presidential campaign: to get France back on its feet and bring the French together."
Opinion polls now show Fillon, a clear favorite until the jobs scandal erupted, is unlikely to reach a second round run-off, in which centrist Emmanuel Macron is seen beating far-right party leader Marine Le Pen.
In a sign that the fake jobs allegations might continue to dog Fillon, French TV showed images of a few protesters banging on pots and pans on Wednesday as he visited Juvisy-sur-Orge south of Paris as part of his campaign. On Tuesday hecklers greeted him during another visit with cries of "Crook! Thief!"
Uncertainty over the outcome of the election, which takes place in two rounds on April 23 and May 7, has this week driven the premium that investors demand for holding French over German government debt to multi-year highs.
Heavyweight centrist Francois Bayrou, who has not yet announced whether he will enter the presidential race, accused Fillon of being under the influence of "financial powers" and said French democracy was under threat.
After apologizing on Monday for having employed family members, and with Wednesday's letter to voters, Fillon's new strategy includes attacking the legitimacy of the financial prosecutor's office investigating the fake jobs allegations.
The investigation is "void", Fillon's lawyer Antonin Levy told journalists on Tuesday, in a change of tack after Fillon had said he welcomed the probe and wanted it to be concluded as quickly as possible.
Fillon has said he would drop out of the presidential race if put under formal investigation. The investigation is so far a preliminary one and it is unclear when it will be over.
Fillon's troubles started when the satirical weekly Le Canard Enchaine reported that Fillon's wife Penelope had received public money for work she may not have done. It later said two of his adult children had also received taxpayer money.
Fillon has said his wife did work for him.
On Wednesday BFM Business, a TV channel, said in an article on its website that Fillon was paid 200,000 euros in fees by insurance company AXA between mid-2012 and mid-2014 via his consultancy business 2F Conseil.
French media speculated at the end of last year that former AXA <AXAF.PA> chief Henri de Castries could become finance minister.
AXA and Fillon's entourage did not reply to requests for comment.
A source in France's governing Socialist Party said grandees in Fillon's The Republicans party were unlikely to topple him now, given that no clear alternative candidate had emerged and that time had run out to organize a new primary contest.
"They weren't far (from a party coup), but they got stuck," the source said.
(Reporting by Michel Rose and Ingrid Melander; Additional reporting by Chine Labbe and Emmanuel Jarry; Editing by Janet Lawrence and Gareth Jones)