* Macron holds his position as election favourite after debate
* He and Le Pen clash over Europe
* First round set for April 23, with runoff on May 7
By Michel Rose and Ingrid Melander
PARIS, April 5 (Reuters) - Centrist Emmanuel Macron kept his position as favourite to win France's presidential election after a televised debate on Tuesday night in which he clashed sharply with his main rival, Marine Le Pen, over Europe, just 19 days before the election.
Macron was seen as having the best political programme, according to a snap survey that also placed him as the second most convincing performer in a four-hour marathon that involved all 11 candidates.
Criticizing Le Pen, the leader of the National Front who wants to leave the euro, hold a referendum on European Union membership and curb immigration, Macron said: "Nationalism is war. I know it. I come from a region that is full of graveyards."
The centrist, who voiced his strong pro-European views, comes from the Somme region, a major battlefield in World War One.
Le Pen hit back at Macron: "You shouldn't pretend to be something new when you are speaking like old fossils that are at least 50 years old."
Macron retorted: "Sorry to tell you this, Madame Le Pen, but you are saying the same lies that we've heard from your father for 40 years."
The comment appeared to be a swipe at Le Pen's efforts to clean up the image of the party her father, Jean-Marie Le Pen, founded and make it more palatable to mainstream voters.
In the Elabe snap poll taken when the debate ended in the early hours of Wednesday, firebrand leftist Jean-Luc Melenchon, a veteran of France's political circuit, took first place as the most convincing performer.
Le Pen lagged in fourth place behind Macron and Francois Fillon.
Macron was seen in the same poll as having the best programme of all the candidates by 23 percent of viewers, followed by Melenchon, whose ratings have been rising since the first televised debate in March, to the detriment of Socialist Party candidate Benoit Hamon.
While the Elabe poll did not show voting intentions, other surveys have consistently shown Macron and Le Pen qualifying for the May 7 runoff and Macron winning it. The high level of undecided voters means the ballot remains unpredictable.
The race for the Elysee has been one of the most unpredictable in memory, with twists and surprises in which some big players have been marginalised and scandal has tainted others.
Macron himself is a former banker who has never held elected office and heads a fledgling political movement called En Marche ! (Onwards!) which has no seats in parliament.
Scandal surrounding Fillon, the main centre-right candidate, and a Socialist party in disarray, have been gifts to his campaign.
Le Pen, a far more established fixture on the political scene, is expected by many to lead in the first round before being beaten by Macron in the May runoff.
In a debate that also discussed trade, immigration and security, Fillon and Le Pen came in for stinging attacks from two far-left candidates, who cited the judicial investigations facing them.
"Since January, it's just been a great campaign ... the more we dig, the more corruption there is, the more cheating there is," said Philippe Poutou, a fringe candidate.
He was referring to a report in the satirical Le Canard Enchaine weekly that was the first to allege that Fillon had been paying his wife huge sums of taxpayers' money for work she had not properly carried out.
Fillon, a 63-year-old conservative former prime minister, and his wife are being investigated over the allegations, although they deny any wrongdoing.
Le Pen in February used her immunity as EU lawmaker to refuse to go to a police summons over allegations she had made illegal EU payments to her staff.
Nathalie Arthaud, another far-left candidate, said: "Supermarket cashiers can be fired just for stealing a voucher. There is a shocking discrepancy here."
It was unclear whether a final debate scheduled for April 20 would take place, after several of the leading candidates said it was being held too close to the election itself. (Additional reporting by Simon Carraud and Elizabeth Pineau; Writing by Ingrid Melander; Editing by Richard Balmforth and Peter Cooney)
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