Rival factions vied to assert control over France's main opposition Socialist Party yesterday and install a leader capable of challenging right-wing President Nicolas Sarkozy.

Segolene Royal, who lost to Sarkozy last year, is standing for party secretary at an acrimonious congress in the eastern city of Reims. But rival leaders who blame her for the party's third defeat in as many presidential elections are engaged in talks to try to find an alternative.

The stakes are high for the Socialists, who have been so busy arguing amongst themselves that they have lost credibility as an opposition force to a president cultivating a high profile in foreign as well as domestic policy.

"We are going to have to cure ourselves, to heal these small and big wounds we have inflicted on each other ... and one day, to forgive one another," Royal told thousands of party members packed into the congress hall.

Royal arouses passions in her party and her speech was greeted with cheers and jeers in equal measure.

The party is under pressure to produce a strong leader and clear policy line, or it risks further alienating voters and losing yet another presidential poll in 2012. Some supporters have even voiced fears the party could fall apart.

A pre-congress vote by party members last week on competing "motions", or broad policy proposals, showed grassroots divisions and failed to give any leader a decisive advantage.

Royal's motion came first with just under 30 per cent of votes, while Paris mayor Bertrand Delanoe scored 25 per cent and Martine Aubry, an ex-minister known for launching the 35-hour working week law, also scored 25 per cent. A younger leader positioned on the party left, Benoit Hamon, came fourth with 19 percent.

One source of discord is the issue of whether to form an alliance with centrists for the presidential poll in 2012.

Royal, the only leader to favour such an alliance, said in her speech that if elected to head the party she would put the question directly to members to end the argument.

"That way, the issue can no longer be used as a pretext by those who refuse to unite around the motion that came out on top," she said in one of her more combative moments.

At other times, she urged Socialists to "love one another" - to mocking boos from many in the hall.

Royal is trying to overcome animosities to forge an alliance that would be endorsed by the congress, which ends today.