* UMP rivals in vicious dispute over leadership contest
* Crisis threatens to tear conservative party apart
* Sarkozy due to meet his former PM Fillon
PARIS, Nov 26 A co-founder of France's opposition conservative party begged former President Nicolas Sarkozy on Monday to step in and save it from implosion after talks failed to settle a vicious dispute over who won last weekend's leadership contest.
Alain Juppe, a former prime minister and veteran of the centre-right, abandoned his bid to mediate in the week-long crisis after a fruitless meeting on Sunday with warring UMP rivals Jean-Francois Cope and Francois Fillon.
Fillon is mounting a legal challenge to Cope's razor-thin victory and the row threatens to tear apart a party whose mission when it was founded a decade ago was to tie together the centrist and harder right factions the two rivals stand for.
Sarkozy - widely seen as considering a comeback for the 2017 presidential election despite vowing to quit politics when he lost power in May - was to meet Fillon, his former prime minister, for lunch on Monday to discuss the crisis.
"It seems clear that (Sarkozy) is the only person today with enough authority to propose a solution where I cannot see one," Juppe told RTL radio. "It's in his hands."
Former interior minister Claude Gueant, stressing that a court battle would be the worst possible route for the party, said Sarkozy could make a statement later in the day.
The botched contest to find a successor to Sarkozy has made a laughing stock of a party that held the presidency for 10 years until Francois Hollande's May election win. It is also a boon for the Socialist president as he grapples with a flatlining economy and slumping approval ratings.
The debacle has exposed a deep split over the party's gradual shift to the right on issues such as immigration and religion that could now reshape the political landscape.
At worst, analysts predict a break-up of a party that former President Jacques Chirac founded to keep the right on a centrist path set by General Charles de Gaulle after World War Two.
Even if the party can hold together, the feud risks distracting the UMP for months from its role as the main opposition party, benefiting both the left and the far-right ahead of local elections in 2014.
"It is hard to see how the UMP continues as a party after this," Arthur Goldhammer, an expert at the Centre for European Studies at Harvard University, wrote in his French politics blog. "Clearly this is a saga that will not play out in a day."
Hollande was due to meet Cope, as UMP leader, on Monday to discuss institutional changes but the meeting was postponed after Cope rejected Juppe's suggestion of forming a new, more neutral, committee to determine the result of the Nov. 18 vote.
The UMP appeals committee was due to give its latest verdict on Monday or Tuesday on the vote, which Cope says he won by 98 votes out of nearly 175,000 cast. Fillon says he would have won by 26 votes had about 1,000 overseas ballots not been excluded.
Juppe said it was possible the party could hold a fresh leadership vote, an idea backed by 71 percent of the French public according to an opinion poll published in the weekly Journal du Dimanche on Sunday. Cope said the idea made no sense.
A close ally of Sarkozy who has said he would put his own presidential ambitions on hold should his mentor decide to make a comeback, Cope also said he believed Sarkozy had "no intention of interfering" in the leadership contest.