By normal political standards, it should have been a disastrous week for Jean-Marie Le Pen, leader of the National Front, an extreme right-wing nationalist party that has challenged the mold of French politics.

In rapid succession, the 56-year-old former paratrooper was accused by his one-time best friend of torture and benefiting from a multimillion-dollar inheritance swindle. He landed in trouble with the tax authorities and was barred from France's leading radio station because of allegedly insulting remarks about four journalists of Jewish origin.

To cap it all, he got divorced Wednesday from the woman to whom he had been married for 25 years. In a final verbal dart, Pierrette Le Pen depicted her former husband as a stingy liar who hates women.

Perhaps the most remarkable aspect of all this is that, so far at least, it does not seem to have damaged the National Front leader in the eyes of his supporters. With just five months to go before crucial legislative elections, public opinion polls consistently give his party around 10 percent of the total vote.

Normal political rules do not seem to apply to Le Pen, whose platform is based on vitriolic opposition to immigration, a strong sense of French chauvinism, and calls for law and order. He seems to thrive on controversy. Much of his success derives from his skill in presenting himself as victim of a conspiracy of establishment politicians and the media.

"How does one deal with Jean-Marie Le Pen?" asked the Paris newspaper Le Monde this week, a question echoed by an increasing number of his political opponents. "Attack him and he appears as a martyr for a part of public opinion. Ignore him and he continues, quietly but surely, on his path."

Le Pen aims to win up to 50 seats in National Assembly elections set for March. Such an outcome would confront the moderate right-wing parties with the choice of ruling with the support of extremists or striking a deal with the Socialists.

Regarded just a few years ago as a marginal grouping of political activists, the National Front won nearly 11 percent of the vote in European Parliament elections in 1984. This unexpected performance put it almost even with the traditionally much stronger Communist Party.

Le Pen's continuing electoral appeal was illustrated by a television appearance last week that was watched by about 14 million viewers -- a quarter of the population -- just one day after a slashing attack on his integrity by his former political confidant, Jean-Maurice Demarquet.

In a full-page interview in Le Monde, Demarquet depicted the National Front as "a planet of the apes" headed by a "paranoid pasha." Le Pen responded in the television talk show by describing Demarquet, who also until recently was his personal doctor, as a "notorious lunatic."

The friendship between Demarquet and Le Pen dates back to when both took part in the Algerian war as young right-wing deputies. They made their early political careers together in the "Poujadist" movement, a right-wing party that voiced the frustrations of small shopkeepers and farmers who felt threatened by economic modernization.

The Demarquet interview revived old charges that Le Pen personally had tortured suspected members of the Algerian National Liberation Front during France's last colonial war. His most sensational accusations, however, concerned murky circumstances in which Le Pen inherited a magnificent chateau near Paris from a cement tycoon, Hubert Lambert, in 1976.

Demarquet told Le Monde that he had been asked by Le Pen to treat Lambert, a political sympathizer, for alcoholism and drug abuse. Alleging that his former patient had been "completely manipulated" by Le Pen, he said it was "strange" that Lambert had died shortly after altering his will in favor of the National Front leader.

Asked if he was implying that Le Pen was directly responsible for Lambert's death, Demarquet said: "There is no crime more perfect than making a terminal alcoholic drink."

On television last week, Le Pen said he intended to sue Demarquet and Le Monde for slander. Reacting to his former friend's catalogue of charges, he joked: "And what about the Mexican earthquake? I suppose I was responsible for that, too."

Part of Le Pen's success as a politician, French commentators say, stems from the way in which he has been able to mask extremist positions by a jovial appearance. Polls conducted immediately after Le Pen's appearance on "Hour of the Truth," France's most popular political television show, indicated that there is still considerable support for some of his ideas. About 48 percent of those polled were reported to approve his call for a referendum on helping immigrants return to their home countries.

Forty percent of those questioned said they felt that Le Pen had been "convincing" in replying to the attacks against him, but 45 percent found him "unconvincing."

In speeches during the past week, Le Pen has accused Demarquet of allowing himself to become an instrument in a political campaign against the National Front by the neo-Gaullist Rally for the Republic party. As the leading opposition party, it has the most to lose if Le Pen succeeds in making major inroads into the right-wing vote in National Assembly elections.

Demarquet has attributed his break with Le Pen to personal frictions over the Lambert affair. He said he had refused Le Pen's repeated requests to issue confirmations that Lambert was of sound mind when he drew up his will.

Le Pen's difficulties with the tax authorities also stem from his television appearance. Needled about his considerable wealth, he said it could not be all that great, as he was not required to pay wealth tax.

When newspapers said he had been liable for wealth tax from 1982 to 1984, he claimed that what he had meant to say was that he would not have to pay any more tax this year because of a property settlement with his wife. His wife said that this was "totally false" and that he had given her no money.