* UMP rivals in vicious dispute over leadership contest
* Crisis threatens to tear conservative opposition apart
* Sarkozy meets his former PM Fillon over lunch
* Cope opposes idea of a fresh leadership vote
By Chine Labbé and Catherine Bremer
PARIS, Nov 26 France's conservative opposition party slid further into crisis on Monday as moderate and harder-right factions squabbled over a disputed Nov. 18 vote to find a successor to former president Nicolas Sarkozy.
The UMP party, which lost power in the May presidential election and has been in chaos since last week's vote, affirmed Jean-Francois Cope as its new leader, saying an adjusted ballot count carried out after claims of fraud confirmed his win.
But Francois Fillon, who has been locked in a fierce dispute with Cope for the past week, immediately dismissed the new count as "illegal", saying the internal UMP appeals committee that produced it was biased in favour of his rival.
The public infighting and claims of ballot-stuffing have horrified France and revealed a deep rift between centrist and harder-right wings in a party formed a decade ago with the explicit mission of glueing those factions together.
"Once again, Jean-Francois Cope has proclaimed himself leader by force," Fillon, who was highly popular as Sarkozy's prime minister and viewed as an urbane and reserved figure next to the volatile president, said in a statement.
Monday's result showed that Cope, a disciple of Sarkozy with hardline views on immigration and religion, won the leadership contest by 952 votes out of around 173,000 votes cast.
Cope was initially declared the winner a week ago by just 98 votes. Fillon contested that result, saying he would have won by 26 votes had some 1,000 votes from overseas territories not been omitted by mistake.
Fillon began mounting a legal challenge to Cope's victory on Monday and Alain Juppe, a co-founder of the UMP and former prime minister, begged Sarkozy to step in and defuse the crisis after his own attempts at mediation failed.
"The committee has confirmed my election. It has even recorded a bigger margin in my favour. The result is there. Everybody must now respect it," Cope said of the new score, which discounted contested areas and added votes from overseas.
Cope, who promises to put his presidential ambitions on hold if Sarkozy decides to come back to run in the 2017 presidential election, said he could not imagine that Fillon would continue his legal action against his own party.
Described by conservative daily Le Figaro as "live suicide", the dispute is tearing apart a party founded by former president Jacques Chirac and which held the presidency for a decade until May. The opposition chaos has provided relief for President Francois Hollande as he grapples with a flatlining economy.
"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."
The debacle has exposed a deep split over the UMP'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 founded to keep the right on the centrist path set by General Charles de Gaulle after World War Two.
Even if it holds together, the UMP risks being distracted from its opposition for months by the feuding, benefiting both the left and the far-right ahead of local elections in 2014.
"This bad soap opera has to end because democracy needs an operational opposition," the Socialist Party said in a tweet.
Earlier on Monday, Sarkozy, who had until now steered well clear of the UMP debacle, met Fillon over lunch.
"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."
Two-thirds of UMP supporters want Sarkozy to run in the 2017 election despite his vow to quit politics after his May defeat. Analysts see the feud increasing his chances of a comeback.
Le Figaro urged Fillon and Cope in a front-page editorial to end a "pitiful spectacle" that was an insult to politics.
Juppe suggested the UMP could hold a new vote, an idea backed by 71 percent of the public in an opinion poll in the weekly Journal du Dimanche. Cope said the idea made no sense.