By John Irish and Andrew Callus
PARIS (Reuters) - France's conservatives appeared to be at war with themselves less than 50 days from the presidential election as Francois Fillon clung on to his struggling, scandal-tainted campaign and senior party members fought to oust him as their candidate.
In a drama-filled day, Fillon delivered a defiant speech to thousands of grassroots supporters in central Paris on Sunday, telling them that they would not be robbed of victory.
But pressure mounted for him to stand aside, and yet another poll showed him on course to be knocked out of the election in the April 23 first round, leaving centrist Emmanuel Macron favorite to win a May 7 run-off against far-right leader Marine Le Pen.
Once the frontrunner, Fillon is mired in a scandal over hundreds of thousands of euros of public money he paid his wife to be his parliamentary assistant. He denies allegations she did little work for the money, but suffered a serious blow last week when he learned he could be placed under formal investigation for misuse of public funds.
Speaking on France 2 television's evening news, Fillon was asked directly whether he would stand down.
"The answer is no," he said. "I see no reason to do that. It would lead to a dead end for my political family."
He added, though, that he was open to discussions. "I am not autistic. I want to convince my friends that my program is the only one that can bring about recovery for the country."
Leaders of his party, The Republicans, are preparing for a meeting on Monday evening to discuss the crisis ahead of a March 17 deadline when all candidates must be formally endorsed by at least 500 elected officials. Fillon said he would be present.
After a string of resignations among advisers and backers, the 63-year-old had been banking on a big turnout at the Paris rally to show his detractors that he remains their best hope to win the presidency.
While hailing the support of thousands of tricolor-waving backers who braved pouring rain and chanted for him to stay, he also acknowledged the obstacles facing him.
"I am attacked from all sides and with all consciousness I must listen to you, listen to this massive crowd that pushes me forward, but I must also ask myself about those who doubt me and jump ship," he said.
His party appears divided, with some heavyweights attending the rally and others looking for an alternative.
Christian Estrosi, Valerie Pecresse and Xavier Bertrand, who run three of the country's largest regions, will meet Fillon on Monday to try to find solutions, Estrosi said, naming ex prime minister Alain Juppe as the best replacement.
Jean-Christophe Lagarde, head of the center-right UDI party, which has an alliance with The Republicans, said Fillon would lead to "certain failure" and called for Juppe to take over.
Minutes after Fillon's TV appearance, Juppe said on Twitter he would make a statement to the press on Monday morning. He has previously said he would not run against Fillon's will.
L'Obs magazine, citing sources close to Juppe, said he planned to say that he would not stand for president, irrespective of what Fillon decided. It was not possible to confirm the report.
A Kantar Sofres-OnePoint opinion poll published on Sunday showed Fillon down to 17 percent, well behind Macron and Le Pen in first-round voting intentions, and therefore out of the contest at that stage.
But it also showed that if Juppe replaced Fillon, he would go through and face Le Pen in the run-off, with Macron eliminated in the first round.
(Additional reporting by Adrian Croft, Simon Carraud, Sudip Kar-Gupta, Emmanuel Jarry and Sophie Louet; Editing by Mark Trevelyan)