PARIS (Reuters) - Nicolas Sarkozy, the ex-president now heading France's main conservative opposition, came under pressure from allies and foes on Monday to endorse rival Socialists in a by-election runoff to ensure the defeat of the National Front.
The anti-immigrant far-right party came out ahead with 32.6 percent in Sunday's first round vote for the parliamentary seat in the eastern Le Doubs constituency left vacant by Pierre Moscovici, a Socialist deputy named EU commissioner.
The Socialist candidate came in second with 28.9 percent ahead of the conservative UMP candidate, setting the stage for Socialist-National Front duel next Sunday.
France's mainstream parties have in the past put differences aside to endorse whichever of their candidates stood the better chance of defeating the FN in run-off votes. But Europe 1 radio said Sarkozy - who has said he wants to lure their voters back to the UMP - was reluctant to back either candidate this time.
"The National Front would disfigure France," UMP deputy president Nathalie Kosciusko-Morizet said on BFM TV, adding she was in favor of endorsing the Socialist candidate.
Senior Socialists also called on Sarkozy to set aside traditional political rivalries.
"Why does Nicolas Sarkozy not make a call for the vote? Because he wants to steal votes from the National Front in the (2017) presidential election," Socialist Party chief Jean-Christophe Cambadelis said on LCI television.
"But now its the National Front that's stealing votes from the UMP. I call on the UMP to collectively take up its responsibilities."
Sarkozy and other UMP bosses are set to make their final decision at a meeting of its leadership on Tuesday.
Some conservatives have acknowledged that Sarkozy's return to politics late last year has not given the divided, cash-strapped UMP the boost he had promised. It is still unclear whether he or a rival will secure the party's ticket for the 2017 presidential election.
The Socialist Party has seen its ratings improve after President Francois Hollande was seen to handle well the aftermath of Islamist attacks last month that left 17 people dead in three days of bloodshed.
But it still needs a further boost ahead of local elections in March and regional elections later in the year, in which they risk heavy losses to the National Front.
The loss of the parliamentary seat in the Doubs, an industrial district struggling with high unemployment, would weaken further their control of the National Assembly after the defection of one of their lawmakers to the far-left last month deprived them of an absolute majority.
(Reporting by Leigh Thomas; editing by Mark John)