By BBC News Online's Henri Astier

For the past five years, Socialist Prime Minister Lionel Jospin has governed France under the banner of the "plural left", in alliance with Greens and Communists.

A glance at the list of candidates in the presidential election makes it obvious how "plural" the French left has become.

No fewer than eight politicians are competing for left-of-centre votes, representing every shade of progressive opinion from mild liberals to red-hot Trotskyists.

Political division is not a problem for the left alone. There are eight candidates on the right as well.

Such divisions are a product of France's two-part electoral system.

Arlette Laguiller attracts protest votes

First-round results reflect each candidate's proportion of the votes, which encourages the ambitious to test their popularity - before the ruthless logic of the first-past-the-post rule forces voters to choose between one of two frontrunners in the final round.

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But a dispersed electorate presents more of a challenge for Mr Jospin than it does for the main conservative contender, Jacques Chirac.

While Mr Chirac's centre-right rivals are marginal, Mr Jospin finds it much harder to ignore the left-wing candidates snapping at his heels.

Flamboyant rival

The main ones are not official members of the "plural left", but anti-establishment candidates who could attract many protest votes.

In the old days, Communists could be wheedled into union - but Mr Jospin's new challengers on the left may not be bought off so easily

The most flamboyant of Mr Jospin's rivals is Arlette Laguiller, a Trotskyist veteran of four presidential campaigns.

Generations of voters fondly remember her televised appeals, prefaced with the quaint form of address "Workers..." - made more melodious in French by the need to include both genders ("travailleurs, travailleuses...").

Ms Laguiller is popular not because of her programme - very few French people believe banning compulsory redundancies and expropriating capitalists are a good idea.

But her sincerity and commitment seem to set her apart from mainstream politicians, and she is a rallying figure for those who think that in government socialists have become indistinguishable from conservatives.

Voters are shunning Communist Robert Hue

Ms Laguiller's popularity is at an all-time high, with up to 10% of voting intentions. That is about twice the score of the Communist candidate, Robert Hue.

This represents a major shift.

Until the 1970s the French Communists were the largest single force on the left. They then went into steady decline and are now shadow of their former selves, both electorally and ideologically - unlike his pro-Soviet predecessors, Mr Hue is little more than a hardline socialist.

This means that the strategy which the French Socialists have adopted for three decades - union with a Communist Party - is no longer enough.

Jean-Pierre Chevenement would be hard to bring into an alliance

In the old days, Communists could be wheedled into union by promises of ministerial jobs, policy concessions, and revolutionary rhetoric.

Such tactics suited the French Socialists, who unlike Germany's SPD or Britain's New Labour have never wholeheartedly converted to the market economy.

But Mr Jospin's new challengers on the left may not be bought off so easily.

Theirs is a politics of commitment. It is hard to imagine Ms Laguiller giving up the struggle for "workers' democracy" in exchange for a ministry.

Likewise Jean-Pierre Chevenement, a left-wing maverick credited with around 8% of voting intentions, cannot be easily co-opted into an alliance.

After initially courting the centre, and saying his programme was 'not socialist', Mr Jospin is now highlighting his differences with the right

Even the Greens, who are government partners, have made clear they should not be taken for granted. Their candidate, Noel Mammere (7%), is pushing an anti-nuclear agenda.

All this has led Mr Jospin, whose campaign seems to be flagging, to revise his tactics in recent weeks.

After initially courting the centre, and saying his programme was "not socialist", Mr Jospin is now highlighting his differences with the right - in effect telling supporters of Ms Laguiller and others he is their man for the second.

For French socialists, focusing on pacifying the radicals, while assuming that moderate voters will not take their hardline rhetoric too seriously, has been a winning strategy in the past.

But in those days the Socialists' partner/rivals were disciplined Communists. Whether the same strategy can work with an unruly bunch of disparate dissidents will be tested in the second round.