PARIS (Reuters) - Former prime minister Manuel Valls is favorite to represent the Socialists in the French presidential election, an opinion poll showed on Thursday, an outcome surveys show would offer the best chance of victory for the beleaguered party and its allies.

Valls is seen coming top in the Jan 22 first round vote of the primaries of the French left with 43 percent, ahead of second placed Arnaud Montebourg on 25 percent, and third-placed Benoit Hamon on 22 percent, the poll by Harris Interactive for France Televisions showed.

He would go on to win the official left-wing ticket by beating either of these two opponents in a run-off on Jan 29, with between 55 and 57 percent of the vote, according to the poll - a similar outcome to others conducted in December.

If Valls, prime minister until a month ago, does emerge the as Socialist candidate, it will fall to him to try to rally the Left and turn the tide against what seems likely to end in a showdown between centre-right and far-right candidates.

But surveys about primaries have proved deceptive in the past.

Polls were predicting a completely different outcome from the actual result in the months leading up to the conservative primaries last November. They had Alain Juppe as favorite over fellow former prime minister Francois Fillon.

In the space of two weeks, Fillon came from third place in the polls to emerge as favorite, and went on to win the ticket for The Republicans party by a big margin.

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Polls predicting the election itself consistently see a likely second round head-to-head between Fillon and National Front leader Marine Le Pen, with the 62-year-old Fillon winning by a comfortable margin. An Elabe poll for Les Echos newspaper reaffirmed that on Thursday.

Regardless of which candidate they end up with, the Socialists, whose prospects of retaining the presidency have suffered from President Francois Hollande’s deeply unpopular rule, were putting a brave face on their chances on Thursday.

“We are the last to get organized for the presidentials. We will be the key to it,” party leader Jean-Christophe Cambadelis said on Europe 1 radio.

Opinion polls of voting intentions for the presidential election itself give Valls or any candidate from the ruling party very little chance of winning.

Hollande’s dismal record on tackling joblessness remains at the front of voters minds, and with two heavyweight rivals hemming him in on the left and the right, the race is looking like an uphill struggle for Valls or any candidate who represents the Hollande legacy.

Polls have consistently put Valls in a distant fifth place and eliminated in the April 23 first round of the election.

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Nevertheless, they show the 54-year-old, who is from the right of his party and quit as prime minister to focus on a presidential campaign, represents the Socialists’ best bet.

On the campaign trail, Valls has shifted to the left in some policy areas, but still has centrist credentials.

“Valls has the merit of mobilizing centre-left voters, which Montebourg and Hamon can’t,” Claude Dargent, a researcher at Sciences Po university in Paris told Reuters.

Elabe’s poll confirmed Valls in fifth spot, with a vote of between 12 and 13 percent in scenarios that included him. But those scenarios that assumed ex economy minister Montebourg or former education minister Hamon in his place produced much lower votes - of between 6 and 9 percent.

HEMMED IN

In front of Valls in the main election polls, aside from Fillon and Le Pen, are two people who have to some degree stolen the Socialist party’s clothes.

One is the centrist Emmanuel Macron, an unelected 39-year-old former investment banker who quit as economy minister in November, turning his back on the governing Socialists who brought him to power to launch his own political movement called ‘En Marche’, which translates as ‘Forward’, or ‘Onwards’.

Elabe showed him gaining on Fillon and Le Pen compared with a month ago, even though the two remained in first and second place in most scenarios.

The other is veteran left-winger Jean-Luc Melenchon. He quit the Socialist party in 2008 to create his own Parti de Gauche (Party of the Left) and has also bypassed the official left wing primaries. Elabe put Melenchon consistently in fourth place.

“In these conditions, with no plan and no electoral advantage, what is a Socialist party candidate for?” asked Melenchon in an interview with Le Monde newspaper.

Thursday’s Harris Interactive poll was conducted online between Jan 2 and Jan 4 among 6,245 people of voting age, of whom 478 registered voters said they would definitely vote in the primary.

Elabe polled 995 people on Jan 3 and 4.