By Clare Murphy BBC News Online correspondent in Paris

With the exception of a few die-hard far-right loyalists, no-one seriously believes that National Front leader Jean-Marie Le Pen will defeat the conservative President Jacques Chirac in the second and final round of the presidential elections on Sunday.

It's a terrible choice to have to make... I will vote for Chirac - the only way I can bring myself to do this is to see this vote as a referendum on Le Pen

French voter Laurent Deviers

France's left-wing leaders have called on their supporters to swallow their pride and do the unthinkable - cast their ballot for Mr Chirac and give the incumbent a further five years of presidential immunity from the state prosecutors investigating allegations of corruption against him.

"Mr Chirac says Mr Le Pen does not believe in democracy and the republic - but frankly I've often doubted whether Mr Chirac does either," said Laurent Deviers, a 29-year-old IT specialist who voted for Green candidate Noel Mamere in the first round of elections on 21 April.

Like others who cast their vote for the spectrum of minor candidates in the first round, Laurent had nonetheless expected Socialist Prime Minister Lionel Jospin to comfortably enter the second round, where he would challenge Mr Chirac for France's most prestigious position.

"It's a terrible choice to have to make, but it has to be done - I will vote for Chirac. The only way I can bring myself to do this is to see this vote as a referendum on Le Pen. And I'm voting no."

Legitimate victory?

The left-wing endeavour to turn the second round into a plebiscite on the far-right has irritated supporters of Mr Chirac, who want his widely anticipated victory to be treated as a legitimate triumph.

But analysts say the margin by which he defeats Mr Le Pen will prove crucial, both to his own standing during his next term as president of the republic and for Mr Le Pen's National Front, which would enter June's legislative elections in a strong position if it had a sound performance in the presidential poll in hand.

It's not impossible that [Mr Le Pen] could emerge with 30% of the French electorate behind him

Jean Viard, Cevipof institute

French polling institutes, embarrassed by their failure to predict Mr Le Pen's success in the first round of the ballot, have refused to publish anything except the most cautious estimates in the run-up to the final vote - giving Mr Le Pen, who took 16.86% in the first round, a score ranging from 19% to 26% in the second.

Nearly 20% of the votes in the first round went to far-right candidates, the majority to Mr Le Pen, and just over 2% to the leader of the National Republican Movement, Bruno Megret.

"This means that if Mr Le Pen scores more than 20% in this last round he is stealing votes from the areas of the electorate which did not initially opt for the far-right," Jean Viard, head of research at the Cevipof institute in Paris, says.

"And this is not impossible - indeed it's not impossible that he could emerge with 30% of the French electorate behind him - picking up votes from the millions who abstained in the first round, and from extremist supporters who voted for the far-left in the first round."

If this were the case, said Viard, it would have serious implications for the parliamentary elections in June.

"That support would translate easily onto the National Front candidates standing in the legislative elections, and turn the party into a real force to be reckoned with."

Apathy

But not everyone has been moved by the furore that has gripped France, and Europe, since the news first broke of Mr Le Pen's shock success on 21 April.

"To be honest I don't really care who becomes president. I'm not that interested in politics," says Soizic Bonjean, who works for a fashion company in Paris.

Soizic Bonjean does not intend to vote in the second round, either

"I don't like Le Pen - but my family and some of my friends vote for him," she says.

"They're not extremists, they're just fed up with the choices that are on offer - it was a protest vote, a wake-up call - and perhaps the Chiracs and Jospins of this world should listen to it."

Soizic was one of more than 10 million registered voters who did not cast their ballot in the first round - a record abstention rate for France, which has a history of strong political engagement.

She does not intend to vote in the second.

There are no estimates as to how many others will stay away from the ballot boxes on Sunday, either in disgust at the limited options on offer, or in continuing indifference as to who will on Monday prepare to take up or resume the position of France's head of state.