By Richard Balmforth
PARIS (Reuters) - France faces a week of political uncertainty with Francois Fillon, the rightwing presidential candidate, under mounting pressure to quit the race because of a fake-jobs-for-the-family scandal and divisions over whether, and how, to replace him.
As Fillon's two closest rivals, the far-right's Marine Le Pen and independent Emmanuel Macron, began vigorously campaigning, the former prime minister appeared to believe he could ride out the storm engulfing his faltering campaign.
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Fillon said he would fight to the end to defend his position as the party's nominee. A source in his camp said he would likely reinforce that message on Monday.
Defying opinion polls that show a dizzy downward slide to a point where the one-time favorite is now trailing in third place, he told supporters: "Hold the line."
"We'll get through this ordeal together and march on to victory," he said in a video message on Facebook.
Fillon's camp on Saturday distributed 3 million leaflets entitled "Stop the Manhunt", painting the scandal as a left-wing conspiracy and declaring: "Enough is enough".
The 62-year-old, a champion of free-market policies to reinvigorate France's heavily regulated economy, has seen his campaign unravel in the two weeks since newspaper Le Canard Enchaine reported his wife Penelope had been paid hundreds of thousands of euros as a parliamentary assistant for work she had not really done.
Seen two weeks ago as the comfortable favorite to win the keys to the Elysee palace, opinion polls now show Fillon failing to reach the May 7 runoff vote.
It has been a humiliating reversal of fortune for Fillon, a devout Catholic and father of five children, who had campaigned as an honest politician.
Since the scandal broke, he and his wife have been interviewed by the fraud police, his office in parliament has been searched, and the inquiry has now been extended to two of his grown-up children.
The accusations also sit uncomfortably with his economic plans for setting France back on to its feet include slashing public spending and sacking half a million public servants.
If he is forced to quit as the center-right's nominee, it would be unprecedented in six decades of French politics.
The stakes are high for France's Right which had looked likely to return to power after five years of Socialist rule under President Francois Hollande.
The prospect of an upset win by Le Pen and her anti-immigrant, anti-EU National Front or by Macron, who has never held elected office, sends shivers too through many Western governments after the Brexit vote in Britain and the election of Donald Trump in the United States.
In the city of Lyon, Le Pen told thousands of flag-waving supporters that she alone would protect them against Islamic fundamentalism and globalization if elected president.
Macron, also in Lyon, focused his attacks on the woman who is now his main rival - calling her policies a betrayal of French values of liberty, fraternity and equality.
The Fillon crisis exposes deep rifts within the alliance of centrist and right-leaning politicians his candidacy represents and there is little sign of consensus on an emergency replacement.
Party officials have said there is probably not enough time to organize a new primary election like the one Fillon won.
Names in the frame for a hasty appointment include Alain Juppe, an ex-prime minister, and former president Nicolas Sarkozy, who came second and third respectively in November's selection contest. But it was not clear how a new nominee would emerge.
Others are Francois Baroin, a former finance minister, and Xavier Bertrand, a former labor minister.
Two deputies from Fillon's The Republicans party have called on him to withdraw and were joined on Sunday by heavyweight centrist Francois Bayrou. Others have expressed loyalty to him.
Political commentators said The Republicans may formulate a clear plan on Tuesday after the party's deputies have reported back from their constituencies on how Fillon is perceived.
(Additional reporting by Brian Love, Emmanuel Jarry, Maya Nikolaeva, Ingrid Melander and Yann Le Guernigou; Editing by Andrew Callus and Richard Lough)