If he accepts his punishment, Mr Le Pen will be prevented from leading the French far-right in the European elections next year, opening the way for his arch-rival, Bruno Megret, to claim the job. This could unleash a vicious war within the NF, the most powerful far-right party in Western Europe.
If he lodges a further appeal, delaying his sentence, Mr Le Pen, 70, risks being banned from running in the next presidential election in 2002. The likelihood of missing out on his fifth run for the presidency would have been much greater if his original two-year ban had been maintained.
It seems likely Mr Le Pen will seize the opportunity to check the rise of Mr Megret by lodging another appeal with the Cour de Cassation, France's highest appeal court, thus postponing his punishment.
The regional appeal court in Versailles decided yesterday that the National Front president was guilty of assaulting a Socialist candidate during the general election campaign in May last year. Mr Le Pen was captured on television footage screaming in the face, and grabbing the clothes, of Annette Peulvast-Bergeal, in Mantes-la-Jolie west of Paris, where she was running against the NF leader's daughter, Marie-Caroline.
Mr Le Pen, who has five days to appeal, dismissed the court's decision yesterday as "slimy". His previous three-month suspended prison sentence was maintained but his fine was cut from 20,000 francs (pounds 2,200) to F5,000. He described his attack on the Socialist candidate as "a derisory incident" and claimed he had been the victim of an "ambush" by the "Socialo-Communist political forces, now running France".
In fact, he was seen by scores of witnesses - including your correspondent - deliberately jumping out of his limousine into a crowd of anti-NF demonstrators and making directly for Ms Peulvast-Bergeal.
NF supporters all over France were being called to a series of sound- linked rallies last night in which Mr Le Pen intended to denounce the court's decision. The supporters were being instructed to go on to the streets and plaster France with 40,000 posters reading: "Avec Le Pen, contre l'injustice" (With Le Pen, against injustice).
The rallies were partly an attempt by Mr Le Pen to bolster internal NF support against Mr Megret. If banned from leading the NF list in the European elections, Mr Le Pen has said that he expects the top spot to go to his wife, Jany.
Mr Megret, a pragmatist who has built his own power base within the party, has said that he will challenge that decision and expects to take the job himself.