If you’re looking for an omen concerning how the French government will deal with what it calls a new kind of anti-Semitism in the country, take a look at its determination to bring hard-nosed reform to its enfeebled economy.

Pierre Gattaz, the head of Medef, the French employers’ association, offered this update last month: “The country’s economic situation is catastrophic. If France were a business it would be close to liquidation.”

President François Hollande, once quoted as saying the economic cycle would assure a recovery—think of sunrise and sunset—announced “a pickup” three weeks ago. Since then, the president has been undercut by his own national statistics agency, which lowered probable French growth this year to 0.7%—hardly enough to stabilize joblessness at 10% or to meet the European Union’s requirements for members cutting their deficits and debts.

This self-propelled economic failure can be rationally explained through an irresolute government’s incompetence, creating a vast crater in its authority.

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Not reassuring: The National Front?s Le Pen leads in a new presidential poll. Zuma Press

But the treatment of the anti-Semitism that has taken root in that crater is of another dimension, embarrassing and inadequate. The problem isn’t really new, and it is easily identifiable as bred in the housing projects at the edges of big cities where France’s five-to-seven million Muslims live. In a country tortured about its declining status and identity, anti-Jewish violence and hatred have now stabbed at French civilization’s lingering notions of universality—while the excesses are being handled with maybe-this-will-go-away caution.

The left-of-center of Le Monde, the newspaper of the French establishment, gave the impression of discovering sliced bread when it wrote in a front-page editorial: “You’ve got to stare the truth straight in the face: There’s a new anti-Semitism in France. It’s as repulsive as what raged in Europe in the 20th century.”

Put Prime Minister Manuel Valls on the right (verbal) side of history, too. After the exposure of anti-Semitism built into pro-Palestinian demonstrations in Paris and its suburbs, he correctly described viciousness existing behind a facade of anti-Zionism and criticism of Israel.

Still, Mr. Valls continues to trade in obfuscating French myths. “There’s only one community,” he has proclaimed, “the national community, which has to gather around our motto of brotherhood and the ideal that is France.”

President Jacques Chirac did better than that on the notional liberté-egalité-fraternité scale in 2003, when he said in response to the bombing in the Paris suburbs of an (unoccupied) Jewish school: “Attacking a Jew in France is an attack on all of France.”

Ten years later, the Paris suburbs contain virtually extraterritorial enclaves, run by Islamic puritans, where Gilles Kepel, a respected writer on Muslims in French society, says there is “a will to subvert society morally and juridically.” Pierre-André Taguieff, the country’s foremost researcher on anti-Semitism, describes these areas as the “breeding ground of new anti-Jewish passions as well as a reserve army of anti-Jewish militancy.”

That was a reference to the hundreds of Islamist recruits with a French background now fighting in Syria and Iraq. The Socialist government fears they will return to France as active terrorists.

But to publicly connect them to future and potentially deadly anti-Semitic outbursts—the suspect in the June murders at the Jewish Museum in Brussels is a Frenchman, who had served with Islamists in Syria—seems a link too far for either Mr. Holland or Mr. Valls to make.

Both have been accused of Islamophobia, of “stigmatizing” all Muslims and, initially, of favoring Israel in the Gaza conflict. Result: Three weeks after the war’s start, Israel now sits in official French Cold-Shoulderland.

As for the French press, next to no mention is made of consistent international reports that the regimes in Egypt, Saudi Arabia, the United Arab Emirates and Jordan would prefer Israel to crush Hamas. On offer instead: examples of radical-chic journalism flattering Paris’s pro-Palestinian demonstrators.

Even so, 62% of the French have said in a poll that they support police bans on pro-Palestinian rallies that bode violence.

Regardless, after a banned march that took place in Paris on July 26, Le Figaro accused the police, apparently under orders, of holding scores of demonstrators for questioning to pad intervention figures, while ignoring a hard-core of 300 violent thugs.

If this was an in-action gauge of the government’s determination to deal sharply and specifically with the “new” anti-Semitism in the streets—and in the no-go Salafist Muslim suburbs—it reflected Mr. Hollande’s generally pathetic projection of authority during his two years in power.

Marine Le Pen, whose traditional far-right National Front voters like neither the Arabs nor the Jews, said the situation illustrated the “incapacity of the state to maintain order.”

Nota bene: This is happening in France, where long August vacations can clear minds, but not of rage and hatred.

According to a poll last week, if a presidential election scheduled for 2017 were held now, Ms. Le Pen would win the first round of the two-stage vote, defeating every plausible candidate. The poll didn’t indicate how the final round would turn out. Which should reassure no one.

Mr. Vinocur is former executive editor of the International Herald Tribune.