For Arab intellectuals, the world-renowned Hungarian-born author, Arthur Koestler, who died in 1983 at age 78, has long been a hero. Koestler, who was a Jew, wrote a book entitled "The Thirteenth Tribe: The Khazar Empire and its Heritage," which debunks the Jewish historical link to what is now Israel and Palestine. Ever since its publication in 1976, the book has been a major ingredient in the perennial Arab/Muslim campaign to discredit Zionism. That Koestler was a Jew, his admirers believe, allegedly gives his book a degree of authenticity.

Koestler's book claims that today's Jewish people are descended not from the ancient Hebrew-speaking inhabitants of what is now Israel and Palestine but from the Khazars, a now-vanished Turkic-speaking people who lived some 2,000 years ago in an area ranging from the Black Sea to the Caspian Sea. Resisting pressures from Byzantium to become Christians and from the expanding Islamic empire to become Muslims, they apparently converted to Judaism in 740 A.D.

They were later wiped out by Mongol forces invading from the east. According to Koestler, the surviving Khazars fled westward to Polish and Lithuanian territories and formed the cradle of contemporary Jewry. It is far more likely that they were absorbed into the neighboring communities of such other Turkic-speaking people as Turkmen and Kazakhs.

Nevertheless, Arab intellectuals have seized upon Koestler's dubious theory to argue, as one commentator explains: "The absolute historical truth is that the Jews did not originate from Palestine. They are not 'descendants' of the mythic Jews of the Bible. Jews from eastern Europe and western Asia were descended from Mongolians and other Asiatic people who had adopted Judaism as their 'religion' over 1,000 years ago and had become known as 'Jews'."

Koestler was an eccentric ideologue. A one-time ardent Communist, he later became a militant anti-Communist crusader. His novel, "Darkness at Noon," is widely regarded as a classic work of anti-Communist literature. A former Zionist who lived in British-mandated Palestine during the early 1930s, Koestler eventually became a fierce opponent of Jewish statehood. Not surprisingly, his book, "The Thirteenth Tribe," was quickly embraced by anti-Zionist activists.

The book focuses on Yiddish- and German-speaking Ashkenazim, the largest Jewish ethnic sub-group. It ignores the existence of Sephardim, descendants of the Jews who fled Spain and Portugal in the 15th Century, and of Mizrachi or Eastern Jews who lived in Iraq, Iran, Yemen, and other Middle Eastern regions--all of whom, like the Ashkenazi Jews, have always claimed ancestral roots in Palestine.

But there is an even more fundamental flaw in Koestler's Khazar theory of Askenazi origins. He claims that the people who escaped the Mongol hordes fled western into Europe from Asia. However, the fact that they spoke Yiddish, a Germanic-based language or German itself--many of them also bearing Germanic names--clearly demonstrates that the Jews migrated eastward from German-speaking territories in western Europe into Poland, Lithuania, and other east European countries.

The issue has, of course, become academic. Israel is now a thriving nation of more than 5 million Jews possessing cultural strains from many foreign regions, but with no evidence of any Khazar influence. But until the Arabs abandon the challenge to Israeli legitimacy made by anti-Zionist polemicists like Arthur Koestler, the likelihood of a meaningful peace in the Middle East is not very encouraging.