GENEVA - Not since the 1930s have Jews worldwide been exposed to the kinds of threats that were being vocalized in the streets of major cities in recent weeks. From Washington to Ottawa to Paris, pro-Palestinian demonstrators have repeatedly and chillingly crossed the line of civil protest, chanting in Arabic for the ''slaughter'' of Jews.'' This language should never be tolerated in democratic, pluralistic societies. Civic and religious leaders should instinctively condemn it. But, so far, few have recognized the seriousness of these threats, even when the documented record of assaults on Jews worldwide is growing.

The vitriolic hatred is especially volatile in the current context of heightened violence in the Middle East, where some Muslim religious and Arab political leaders have been calling for holy war, jihad, against Israel - and against Jews.

A sermon in the Al Aksa mosque in Jerusalem, broadcast by the Palestinian

Authority, called on Muslims to ''eradicate the Jews from Palestine.'' And a cleric appointed by the Palestinian Authority, addressing worshipers at Friday prayers, declared: ''Have no mercy on the Jews, no matter where they are, in any country. Fight them where they are. Wherever you meet them, kill them.''

Some among the faithful already believe that they are in the midst of such a crusade, and far from the Middle East they have begun to answer calls for war against the Jewish people. Since early October there have been dozens of attacks on synagogues, schools and other Jewish sites across France, Germany, England, Australia, South Africa and elsewhere in Western Europe, North America and Latin America.

In France alone more than 70 attacks have included destruction of a synagogue, with its five sacred Torah scrolls, near Versailles, desecration of several Paris synagogues and stone-throwing at children going to or from Jewish schools.

Six years ago, Rashid Baz, in an act of revenge linked to events in the Middle East, opened fire on a van on New York's Brooklyn Bridge, killing one of the yeshiva student passengers. That premeditated murder should be recalled now, especially after shots were fired at a rabbi on a Chicago street, and an Orthodox Jew in London was stabbed repeatedly.

Religious rulings, or fatwas, issued by Muslim clerics calling for jihad against Jews wherever they live encourage this terrorism. One fatwa came from Sheikh Omar Abdel Rahman, who is serving a life sentence in a U.S. prison for his role in the World Trade Center bombing.

Another came from a Muslim group in London associated with Osama bin Laden, the terrorist mastermind sought by the United States. This fatwa has been rapidly and broadly sent through the Internet, the ultimate tool for high-speed dissemination of hate.

Western political leaders, shortsightedly, have generally dismissed the verbal threats as mere rhetoric or characterized the attacks carried out to date as random, isolated incidents. They may not be planned by the same source, but the hateful words espoused by religious leaders and the deafening silence of others in the Arab and Muslim communities surely encourage further assaults.

Whatever one may think about the Arab-Israeli conflict, there can be no justification for this outbreak of raw anti-Jewish violence.

Such incidents in Europe and America are strikingly similar to attacks in areas of the West Bank under the control of the Palestinian Authority, including the destruction of Joseph's Tomb in Nablus, the burning of the ancient synagogue in Jericho and the cowardly murder of Hillel Lieberman, the rabbi who tried to save the Torah scrolls at Joseph's Tomb.

Given this contempt for Judaism, imagine for a moment what Palestinian demonstrators might do to Jewish worshipers and the sacred Western Wall itself if they managed to break through Israeli security guarding the entrance from the Temple Mount, Judaism's holiest place for 2,500 years.

With the Palestinian Authority stepping up its pernicious campaign to negate Jewish history by falsely claiming that the Jewish temples never existed on the Temple Mount, and with Yasser Arafat vowing to continue violence until the Palestinian flag is hoisted atop the ramparts of the walled Old City of Jerusalem, the war against Jews is likely to continue.

Responsible political and religious leaders must speak out clearly and unequivocally against this odious and sinister effort to extend the Arab-Israeli conflict beyond the Middle East, and condemn unconditionally the violence and calls for further attacks against Jews.

Law enforcement, slow to grasp the severity of the situation, must step up its response and recognize the dangers of the bloodcurdling injunction to ''slaughter the Jews.''

One of the costly lessons the world should have learned is that words such as these have enormous power. When Hitler wrote Mein Kampf in 1925, calling for the extermination of Jews, few took him seriously. A decade later he began to implement his grotesque plan.

Today's calls for violence threaten not only Jews but also the very foundation and fabric of Western pluralistic societies.

The writer, executive director of the American Jewish Committee, contributed this comment to the International Herald Tribune.