By Adrian Croft and Sudip Kar-Gupta
PARIS, (Reuters) - France's presidential race is tightening in its final weeks with a far-left and a conservative candidate narrowing the gap on long-time frontrunners Emmanuel Macron and Marine Le Pen, two polls showed on Friday.
An Odoxa poll for Le Point magazine showed 23.5 percent of voters set to back centrist Macron in the April 23 first round, a fall of 2.5 percentage points in a week.
Macron was just half a point ahead of far-right National Front leader Le Pen, whose score was down 2 points.
Right behind them, conservative candidate Francois Fillon, whose campaign has struggled against nepotism allegations, gained one-and-a-half points to 18.5 percent while far-left veteran Jean-Luc Melenchon was up two points to 18 percent.
Only the top two candidates go forward to a May 7 runoff, where Macron is tipped to easily beat Le Pen.
Odoxa analyst Gael Sliman said the polls underlined Macron's paradoxical situation. The former economy minister was "assured of winning in the second round, but no longer so sure of qualifying for it," he said in a note.
Many voters, particularly on the left, remain uncertain of who they will vote for, pollsters say.
Le Pen's plans to ditch the euro and hold a referendum on European Union membership have spooked many investors, who fear a "Frexit" after British voters opted last year to leave the EU.
A second poll by Harris Interactive showed Macron on 24 percent, down two points in two weeks, just ahead of Le Pen on 23 percent, also down two points in two weeks.
Fillon was on 19 percent, up one point, but the big gainer was Melenchon who was up 4.5 points in two weeks to 18 percent.
The 65-year-old Melenchon, a skilled speaker backed by several small leftist groups, aims to take France out of NATO and overhaul the EU.
Viewers rated him the most convincing among the candidates in their televised debate last Tuesday. He produces a popular weekly YouTube video and Odoxa said his campaign website had the most hits of all contenders.
He won only 11.1 percent of votes in the first presidential round in 2012, less than what opinion polls had predicted.
Macron, a pro-European former banker who has never held elected office, aims to transcend the traditional left-right divide in French politics and reduce public spending and taxes.
Opponents say he is too inexperienced for the top job.
Bogged down by allegations of financial scandal, Fillon got a boost on Friday from an endorsement by former president Nicolas Sarkozy, whom he beat in the conservative nomination.
"There is no longer any room for hesitation or moods," Sarkozy said on Twitter. "Francois Fillon is the only candidate with the experience to ... bring about the change that France needs so much."
(Additional reporting and writing by Richard Balmforth, Emmanuel Jarry and Dominique Vidalon; Editing by Tom Heneghan)