VIENNA (Reuters) - Far-right parties in some European countries are winning over Jewish voters by exploiting fears about militant Islamists and mainstream parties must do much more to address Europeans' security concerns, a Jewish leader said on Tuesday.

Boosted by Europe's migrant crisis, Norbert Hofer of Austria's anti-immigration Freedom Party only narrowly lost the country's presidential election on May 22. He would have been the first far-right head of state in the European Union.

"I understand that, most probably, a not insignificant part of the (Jewish) community here voted for Hofer for the presidency," the head of the Conference of European Rabbis (CER), Pinchas Goldschmidt, told Reuters in an interview.

Goldschmidt, who is also the chief rabbi of Moscow, said he had received reports of a similar shift among French Jews towards supporting the anti-immigration National Front ahead of presidential and parliamentary elections next year in France.

"When God gave out intelligence, not everybody stood in line. And so when those parties come with a populist message to the Jews and say 'We're going to save you from the Muslims' ... propaganda is effective," he added.

Freedom Party leader Heinz-Christian Strache visited the Yad Vashem Holocaust memorial in Jerusalem in April - a gesture rich in symbolism, given the Nazis' role in Austrian history and the flight or murder of most Austrian Jews following the country's annexation by Adolf Hitler in 1938.

"Not only from the Freedom Party in Austria but also from the side of, for example, the National Front in France ... and also (Geert) Wilders in Holland, they all seem to want us Jews to say they are acceptable," Goldschmidt said.

Today Austria is home to an estimated 15,000 Jews and more than 500,000 Muslims.

"DANGEROUS" POPULISM

The security threat posed by Islamist militants has become much clearer after last year's Paris attacks and must be tackled, Goldschmidt said, adding that Europe's Schengen area of passport-free travel made that more difficult.

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"I think that since the populist right-wing parties raised real concerns of people, unless the mainstream parties of Europe are going to address those issues, they're going to lose."

Goldschmidt, who was in Vienna for a gathering of the CER, suggested measures including the creation of a European anti-terrorism task force, improvements in border security and more effective integration of refugees.

He also condemned what he said was the tendency of far-right parties to conflate ordinary Muslims with Islamist militants.

"(The) moderate Muslim is our natural ally. They are as much the victims of radical Islamism as we Jews. It is the populism, the generalization, which is dangerous and destructive."

(reporting by Francois Murphy; Editing by Gareth Jones)