By John Irish and Emmanuel Jarry
PARIS (Reuters) - Scandal-hit Francois Fillon was set to be confirmed as the conservative candidate in France's presidential election on Friday, despite dismal ratings, as the window for putting an alternative name on the ballot paper closed.
The campaign is one of the most unpredictable in the country's history as opinion polls show almost 40 percent of voters are not completely sure who to back in a topsy-turvy campaign dominated by a fraud investigation into Fillon.
The former prime minister has fought off pressure from his The Republicans party to step aside before Friday's deadline when all presidential candidates must be formally endorsed by at least 500 elected officials.
Once the frontrunner, Fillon has slipped behind far-right National Front leader Marine Le Pen and centrist Emmanuel Macron in the polls, a position that would eliminate him in the first round of the election on April 23.
The fraud investigation into Fillon widened on Thursday to include luxury suits he received as gifts. He is already under formal investigation on suspicion of misusing public funds linked to salaries he paid his wife and children.
The mystery benefactor who paid for two made-to-measure suits for Fillon worth 13,000 euros ($14,000) from exclusive Left Bank tailor Arnys in February was named on Friday as well-known lawyer Robert Bourgi, a judicial source said.
The Senegal-born Bourgi, a confidant and adviser of African presidents and conservative French politicians over decades, declined comment.
Asked for comment, Bourgi told Reuters by email: "I will make no comment and give priority to the judges if they should happen to question me." He was quoted by BFM TV as saying the suits were a gift and he expected nothing in return.
Fillon, 63, has insisted he will fight on despite an Odoxa opinion poll on Friday showing that three-quarters of French voters want him to pull out of the race.
A weekly Ipsos SopraSteria poll for Le Monde on Friday showed Fillon losing more ground to Le Pen and Macron.
The polls point to a May 7 run-off between Le Pen and Macron, with the latter convincingly winning that duel.
Fillon has noticeably begun to use more right-wing language, borrowing phrases from the National Front in an attempt to appeal to its voters.
"I loathe all kinds of racism, including anti-French racism," Fillon said in a speech on Thursday night, using a phrase made popular by National Front founder Jean-Marie Le Pen, father of the party's current leader.
Fillon's main rival for his party's ticket, Alain Juppe, opted not to challenge him, even if theoretically he could still get 500 backers by 1800 local time (1300 EDT).
Fillon, Le Pen, Macron, Socialist candidate Benoit Hamon, far-left firebrand Jean-Luc Melenchon and two lesser-known candidates have already reached the endorsement target.
Another four at least could also reach the goal when the Constitutional Council publishes its final sponsors list.
It will confirm the candidates on Saturday.
($1 = 0.9306 euros)
(Additional reporting by Michel Rose,; Writing by John Irish and Adrian Croft; Editing by Richard Balmforth)