With his ramrod straight back and his piercing stare, Lionel Jospin looks more like a headmaster than a candidate to be France's next president.

He has none of the flamboyance of Jacques Chirac, the mercurial incumbent at the Elysee, who can cuddle pigs and fellow world leaders with equal ease.

Yet Mr Jospin, 64, has made a career out of being underestimated. He has survived almost five years as prime minister under Mr Chirac. That means he is set to become the first premier in the Third Republic to complete a full-term while cohabiting with a head of state of a different political colour.

He also survived the 14-year reign of President Francois Mitterrand, including the humiliation of being overlooked as prime minister in favour of a younger Socialist party rival.

There are fewer than three months left until the first round of France's presidential election and Mr Jospin intends to wait until early March to declare his candidacy.

The delay had at one time exasperated Socialist party friends who urged him as long as 18 months ago to step down as prime minister and prepare his campaign.

But Mr Jospin doggedly refused. His strategy owes something to an unwillingness to let a rival into the prime minister's seat at the Matignon, the most powerful executive post in the country. Mr Jospin knows that running the government insulates him to a degree from the day-to-day campaign. By nature, Mr Jospin is a cautious individual who rarely changes his mind and prefers to stick to a principle, even at the risk of looking outdated.

He came to power unexpectedly in 1997, largely because the centre-right administration of Alain Juppe (a Chirac protoge) mishandled attempts to reform railway pensions, so provoking a wave of industrial unrest.

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Mr Jospin has never forgotten Mr Juppe's fate. But his caution also stems from the difficulties inherent in managing a left-wing coalition government comprising Socialists, Greens and Communists.

This task became harder after the forced departure of Dominique Strauss-Kahn, his talented centrist finance minister. The slowdown in the economy, coming after several years of solid growth and job creation, has made it even tougher.

Mr Jospin's record on economic reform is mixed. Prodded by Mr Strauss-Kahn, he pushed through more privatisations than his predecessor, notably the partial sell-off of France Telecom. But relations with business are at an all-time low, largely because of his insistence on a 35-hour working week.

The shorter working week, which is being expanded to smaller businesses and the public sector, has allowed some companies to demand more flexible working practices. But it has still proved a costly and burdensome exercise.

Socialists explain that Mr Jospin was simply fulfilling a campaign pledge. More important, the 35-hour working week was the price the incoming Socialist-Communist-Green coalition was prepared to pay for industrial peace from the trade unions.

Yet there is some evidence to suggest that ordinary Frenchmen and women, particularly among the younger generation, would be more willing to work longer hours if the reward was lower taxes and higher pay in a more competitive world.

Mr Jospin, a former Trotskyist (though he prefers to gloss over his past), is hard-pushed to style himself a moderniser. But success in the election campaign will depend in part on whether he can appeal to a French middle class torn between accepting and rejecting globalisation.

One of Mr Jospin's closest advisers says that the Jospin government could have done more on economic reform, but he brands the Gaullists under Mr Chirac as the "real conservatives".

Indeed, in a dialectical argument of the sort often favoured by Mr Jospin, this adviser says that the Socialists are the best equipped because they can reform by stealth, without antagonising those constituencies most likely to oppose change.

Mr Jospin deserves credit for managing the difficult cohabitation with Mr Chirac. Olivier Schrameck, chief of staff to Mr Jospin, describes it as two people trying to drive a car, one with a foot on the accelerator, the other with his foot on the brake.

The tension has not always served France's interests. A divided executive has led to different nuances on foreign policy, notably Europe. Even though foreign affairs is the traditional preserve of the president, Europe penetrates domestic policy to such an extent that the dividing line is outdated.

Mr Jospin has never been emotionally committed to European integration and previously entertained doubts about joining monetary union. But he has come to see that France is stronger as part of the European Union rather than as a solo actor.

The next step would be to offer some idea of France's role in a union of 20-plus countries, embracing east and west. So far, with the notable example of a long speech on globalisation delivered in Brazil last year, he has steered clear of big visions and concentrated on the detail of government.