France`s opposition Socialists slid deeper into disarray Sunday after they failed to agree on a new leader and a platform to build a challenge to right-wing President Nicolas Sarkozy.

Segolene Royal, who lost to Sarkozy in elections 18 months ago, accused rivals of clinging to `outdated` ways after they refused to rally behind her leadership bid at a three-day party congress.

It was now up to party members to decide on their new leader during a vote on Thursday, with Royal standing against Martine Aubry, the mayor of Lille and architect of the 35-hour work week, and third contender.

`Party members will now have their say,` Royal said after talks on finding a consensus candidate collapsed in the early hours on Sunday.

`They will have to choose between a return to outdated methods or a new Socialist Party.`

Delegates at the congress in Reims, the capital of the Champagne region, had hoped to unite behind a single candidate who would then be endorsed by the rank-and-file.

But after drawn-out negotiations, no leader emerged with majority support.

Long considered a strong contender to lead the party, Paris Mayor Bertrand Delanoe was forced to bow out of the race after failing to garner enough support.

`The Socialist Party is gravely ill,` he said before announcing that he would not be a candidate for the post of party secretary general `to avoid creating further confusion.`

Royal, the 55-year-old president of the Poitou-Charente regional council, promised to renew the left by opening debate on a possible alliance with centrists, a stance fiercely opposed by the old guard.

While Royal could still win the vote on Thursday, her ability to lead would be badly crippled without the support of party barons and the bickering was expected to continue.

The Reims congress was seen as a last chance for the Socialists to put an end to squabbling and get to work on restoring their credibility under a new leader before the 2012 presidential vote.

But after the party failed to overcome its deep divisions, Sarkozy was left with no strong opponent. His approval ratings have improved recently with his high-profile presidency of the European Union.

Sarkozy`s UMP party declared the congress a `fiasco`, with a spokesman saying the `great Barnum and Bailey circus` in Reims showed the Socialists had `no plan for France and no programme to offer the French people.`

Royal will face off on Thursday against Aubry, 58, the daughter of former European Commission president Jacques Delors, and 41-year-old Euro-MP Benoit Hamon, who has pushed a leftist platform.

A fierce Royal opponent, Aubry pledged to keep the party`s leftist core intact but warned that French voters could turn their backs on the Socialists if they fail to get their act together.

`The French people don`t hate us, but we have let them down,` she said. `We could perhaps be facing the end of the Socialist Party.`

While weakened nationally, the Socialists and their leftist allies control 21 of France`s 22 regions and they made major gains during municipal elections in March.

Royal`s candidacy was propelled by her first-place showing in a vote by party members this month in which her manifesto for the party`s future won nearly 30 percent of the vote, ahead of Delanoe and four other contenders.

Party members are choosing a successor to Francois Hollande, Royal`s former partner and father of her four children, who sided with Delanoe during the leadership battle.

The party congress was held amid much concern over the global economic crisis, with former prime minister Laurent Fabius warning that 300,000 jobs were at stake in France.

`This is an economic and social horror. We need to be ready for it,` said Fabius.