By Sudip Kar-Gupta and Sarah White

PARIS (Reuters) - France's presidential race looked tighter than it has all year on Friday, nine days before voting begins, as two polls put the four frontrunners within reach of a two-person run-off vote.

The latest voter surveys may raise investor concerns about the outside possibility of a second round that pits the far-right candidate Marine Le Pen against hard-left challenger Jean-Luc Melenchon.

The election is one of the most unpredictable in modern French history, as a groundswell of anti-establishment feeling and frustration at France's economic malaise has seen a growing number of voters turn their backs on the mainstream parties.

An Ipsos-Sopra Sterna poll showed independent centrist Emmanuel Macron and Le Pen tied on 22 percent in the April 23 first round, with Melenchon and conservative Francois Fillon on 20 and 19 percent respectively.

That 3 percentage point gap separating the top four was within at least one of poll's margin of error, suggesting the race remains wide open.

Polls have consistently shown Macron would comfortably win the second round should he qualify for the May 7 vote.

But the most striking trend in past days has been the late surge in support for Melenchon, a former Trotskyist who would pull France out of NATO and, like Le Pen, possibly the European Union too.

In the second poll showing the top four within three points of each other, BVA pollsters said: "All scenarios are possible for April 23."

"A second round with Emmanuel Macron and Marine Le Pen remains the most likely hypothesis, but nothing excludes that Francois Fillon or Jean-Luc Melenchon would qualify instead," BVA said.

Polls show that about a third of France's 45.7 million voters might abstain. While some analysts say a higher turnout would favor Macron and Fillon, BVA said the Le Pen and Melenchon could also benefit if young and working class voters cast ballots in high numbers.

Melenchon's progress, and the possibility of a showdown between the founder of the "France Unbowed" party and Le Pen, has alarmed investors. Voter surveys show that, should he reach the second round, Melenchon could win against Fillon or Le Pen.

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Le Pen would not win the presidency whoever she faced in the run-off, polls indicate.

French judges investigating her alleged misuse of EU funds to pay for party assistants have asked for her parliamentary immunity to be lifted, though her legal woes have not been as harmful to her in the polls as the allegations of nepotism that have plagued Fillon's campaign.

A third poll published on Friday showed a six-point gap splitting the four main players in a first-round field of 11 candidates. The daily survey by Opinionway had Macron as leader on 23 percent and Melenchon the laggard on 17.

(Writing by Ingrid Melander and Andrew Callus; Editing by Richard Lough)