By Pauline Mevel and Gregory Blachier
PARIS (Reuters) - Nicolas Sarkozy won the leadership of the conservative UMP on Saturday, a potential step towards a bid to be French president for a second time, but his victory was not decisive enough to cow his rivals in the party.
After losing the presidency to Socialist Francois Hollande in 2012, Sarkozy made a storming comeback in September, although recent polls showed his popularity among members of the crisis-torn UMP wavering.
Sarkozy won 64.5 percent of the vote. Analysts had said before the vote that he needed at least 70 percent to see off rivals and become the party's undisputed champion for the presidential battle in 2017.
He scored 85 percent when he last won the leadership, in 2004.
Alain Juppe, a UMP heavyweight who has said he wants to be its presidential candidate in 2017, was not backing down.
"I am ready to help him of course if we take the course I have set out, rallying the right and the centre," he told reporters after the result.
"We will see for the (presidential) primaries. That's not the subject. The opposite of vigilance is what? It's going to sleep? I am not going to go to sleep."
Francois Fillon, Sarkozy's other main potential rival for the UMP presidential ticket, took a similar line.
"Unity does not mean submission," he said in a statement. "For my part I will defend my convictions."
Sarkozy said the campaign had been "dignified" and took comfort in what he said was a record turnout, calling it in comments on his Facebook page "the best response to two years of internal quarrels and divisions".
The 24-hour online vote was slowed on Friday evening by a cyber attack on the election website, but in the end more than 58 percent of its members had cast a vote, a bigger turnout than in past elections, and party officials declared it fully valid.
With Hollande's ratings sent to record lows by tax rises and a failure to tackle unemployment, the opposition conservatives should be flying high. Economic data last week showed the jobless rate at the latest record high and consumer spending in the doldrums.
But the UMP has long been riven by leadership squabbles, and both it and its new leader are mired in a legal inquiry into alleged funding irregularities.
Although Sarkozy says he is the innocent victim of a politically motivated plot, concerns about the cases have weighed on his ratings.
He is also seen as a polarising figure in French politics, yet UMP eyes are also on another problem - that some of its voters have been lured away by a resurgent far-right National Front led by Marine Le Pen.
Sarkozy's 2014 platform has been aimed at winning voters back from Le Pen and refounding the 12-year-old UMP.
He has sought to appeal to voters worried about multi-culturalism in France, and urged the European Union to hand back all but its core powers to national governments. He also lately vowed to revoke a 2013 law allowing same-sex marriage.
Le Pen is due to be confirmed unopposed as National Front leader at a party congress vote on Sunday. Opinion polls show her as a likely contender in any second-round vote in 2017, where the two highest scoring presidential candidates go head-to-head if no outright first-round winner emerges.
Sarkozy's main challenger for the UMP leadership, Bruno Le Maire, won 29.2 percent. The third candidate, Herve Mariton, received 6.3 percent.
(Additional reporting by Sophie Louet; Writing by Andrew Callus; Editing by Rosalind Russell and Louise Ireland)