The greatest threat to U.S.-Israel relations has nothing to do with a secret American peace plan, settlement construction, a new Intifada, another Arab oil boycott or Palestinian civil war. It is religious extremists -- Jewish, not Muslim.

The latest skirmish in the "Who is a Jew?" wars is taking place in the Knesset Committee on Law and Justice, where two right-wing parties, one secular and the other fervently Orthodox, are writing a new law governing conversion that has many American Jewish leaders worried about the far-reaching impact on support for Israel.

The legislation gives the chief rabbinate, run by the fervently Orthodox, a monopoly on conversions and overturns a High Court ruling providing Israeli citizenship for Jews converted by all branches of Judaism.

Natan Sharansky, who chairs the Jewish Agency for Israel, called the measure divisive, saying that by not recognizing "conversions of other streams of Judaism, it causes Diaspora Jews to feel that they are being made 'illegal.' This is stupidity."

Rabbi Steven Wernick of the United Synagogue of Conservative Judaism has said the law "delegitimizes most of North American Jewry."

Rabbi Eric Yoffie, head of the Reform movement, said the legislation "will cause an anger amid American Jews when Israel needs its support the most."

As the religious establishment's domination spreads across Israeli society, American Jews are increasingly asking, "Why should we work so hard for a cause that says 'we don't respect you, we don't want you and we don't even consider you a real Jew'?"

Prime Minister Benjamin Netanyahu has said the bill will not come up for a final vote, but that could change in the face of pressure from its two principle backers -- the hard-line nationalist Yisrael Beiteinu headed by Foreign Minister Avigdor Lieberman, and Shas, the fervently Orthodox Sephardi Party -- who have the power to bring down his government if they don't get their way.

The new monopoly on conversions is part of a larger problem that threatens Israel-Diaspora relations. Religious extremists are taking greater and greater control of Israeli life. They are disproportionately getting public funding while growing numbers are not working, not paying taxes and not serving in the army.

This conversion law is the latest example of an anti-democratic religious establishment run amok.

Police on Monday arrested Anat Hoffman, leader of Women of the Wall, for carrying a Torah near the Western Wall, a practice forbidden by a High Court ruling and laws passed for the fervently Orthodox who control the area. Worshippers are segregated by gender, and women are forbidden to read from the Torah or wear tallit or tefillin near the Kotel.

Israel's Orthodox establishment has been pushing for laws that forbid the display of chametz in stores and restaurants during Pesach. --

In many communities, bus companies are pressured to segregate passengers by gender.

Jewish success in America owes much to the traditions of religious tolerance and constitutional separation of church and state -- two qualities sadly missing in the world's only Jewish state. With a religious establishment that appears bent on turning Israel into an anti-democratic theocracy and at a time when much has been written about the disaffection of many younger American Jews toward Israel, this is guaranteed to accelerate that exodus.

If it is enacted, the new conversion law could create a severe crisis in relations between Israel and American Jewry that would undermine Israel's support on Capitol Hill by discouraging political activism among the huge majority of American Jews who do not identify as Orthodox.

What motivation would they have to lobby or provide financial support for an Israel that tells them they're not really Jewish?

Admirers say Netanyahu is at heart a political pragmatist. It is time for him to demonstrate that pragmatism by blocking the conversion bill and putting an end to the religious blackmail that threatens the Israel most American Jews care so deeply about.

Douglas M. Bloomfield is a nationally syndicated columnist.