Fifty years ago, a brilliant, 16-year-old high school student called Françoise Quoirez was asked to write a philosophical essay for her baccalauréat entitled 'In what way does tragedy resemble life?' Part of the answer can be found in her first novel, Bonjour Tristesse, written a year later under the nom-de-plume Sagan, and the rest in her own revelations this weekend after four years of silence and suffering.

Only a frail shadow of the carefree adolescent whose first book sold millions of copies worldwide after publication in 1954, Sagan, with the aid of a glass of whisky and several cigarettes, admitted during a television inter view that her health and financial problems were so grave, she was too distressed to finish two books she was preparing to add to her list of 40.

At the root of the biggest personal crisis in a life of extravagant highs and lows, during which she gambled away or squandered several fortunes, was a court order to pay taxes on about £500,000 of undeclared income or go to prison for a year, a threat which came after a fall in which she broke her thigh - an injury that still troubles her after nine operations.

'All my royalties are being paid directly to the "fisc",' she said, referring to the court action by France's inland revenue. 'They don't leave me a euro to live on. I am living on the charity of a friend and I am destined for the hospice.' Some of France's showbusiness and literary establishment, headed by the actress Isabelle Adjani, are trying to save her from that final humiliation in a campaign that amounts to declaring Sagan the equivalent of a classified national monument.

'Françoise Sagan may owe some money to the state, but France owes her much more in return for the prestige that her talent has earned the country from all over the world,' Adjani said after signing a petition which has been backed by award-winning writers including Philippe Sollers, Alexandre Jardin and Régine Desforges.

They want a presidential pardon and a nationally funded scheme to ensure that Sagan lives out the rest of her life 'in an atmosphere of tranquillity so that she can dedicate herself to writing'.

The female prodigy whom the late François Mauriac called 'a charming little monster' was still recognisable by her unchanging hairstyle during her interview with the presenter of a literary programme, Guillaume Durand. But the splash of bright red lipstick, careful make-up and an extravagant necklace could not camouflage the fact that Sagan, 66, looked weatherbeaten and ravaged by problems that have kept her out of the public eye since her last novel, Le Miroir Egaré (The Lost Looking Glass).

'I have been given extreme unction nine times,' she said, referring to recent operations when she had courted death. She was probably speaking figuratively, as the strictures of her Catholic background have long since been overlaid by the experiences of a fast-driving, sexually liberated heavy drinker.

Her most recent biographer, Sophie Delassein, said it had become almost impossible to follow Sagan's life in the fast lane littered with divorces, drug taking, drinking and a bewildering line of lovers or close friends that ran from Tennessee Williams, through Jean-Paul Sartre and François Mitterrand. 'After a bit you quite lose track,' Delassein said.

The young woman who shook middle-class morality with novels such as Un Certain Sourire and Aimez-vous Brahms?, which earned millions, may have exhausted her creative talent except for an ability to seize headlines. During her television appearance she appeared to have lost the plot, despite proffering some insights like the instruction from her rich businessman father that she must spend every franc she earns from writing as fast as possible - an injunction she obeyed to the letter when she was the brightest young figure in Saint-Germain-des-Prés and St-Tropez.

Her preference for men of experience, first expressed as a 17-year-old in Bonjour Tristesse, has been linked to her downfall, which led her to abandon her autobiography.

After a close friendship with Sartre in his last years, she was associated with Mitterrand's entourage, a refuge for mature Don Juans.

Allegedly, she was asked to use her influence with the Socialist President to seek approval for oil concessions in Uzbekistan on behalf of Elf oil.

Claims from the firm that a huge kickback had been paid to a Swiss bank account - which Sagan denied - were at the root of the tax-dodging prosecution.

Sagan tried to clear the air on television by saying she was the innocent victim of a scam which ended with her Normandy house - the setting for many personal and literary dramas - being seized and sold by auction. The interviewer admitted being baffled when Sagan descended into mumbling whenever pressed for detail.

Apart from the shock of seeing the former golden girl of European literature so diminished, the most surprising part of the interview was her unfavourable reaction to questions about 'literature of the body', sexually explicit contemporary feminine writing headed by Catherine Millet, seen in France as the inevitable outcome of the libertine atmosphere pioneered by Bonjour Tristesse .

'I don't like it at all,' Sagan said, pulling hard on a cigarette.