Recurring “who is a Jew” crises pitting many American Jews against fervently Orthodox leaders in Israel and their Knesset friends may be contributing to a seismic shift in the base of the pro-Israel movement in America.

That was one factor spurring the unusual involvement of several Jewish lawmakers in Washington who last week took the dramatic step of writing to Israel’s U.S. ambassador and imploring his government to block a proposed law that critics say would codify the role of fervently Orthodox rabbis in determining the country’s policy on conversion to Judaism.

While most Jewish leaders expect the current legislation to be modified or postponed — especially now that Prime Minister Benjamin Netanyahu has announced strong opposition — some see the controversy as part of a longstanding pattern that is contributing to the widely documented detachment from Israel taking place mostly among secular, Reform and Conservative Jews.

“It’s like a Chinese torture — drip, drip drip,” said Thomas Dine, the former executive director of the American Israel Public Affairs Committee (AIPAC). “Eventually, these things begin to wear out the enthusiasm of American Jews for the Jewish state.

“That was always my worry, and it continues to be my worry,” Dine continued. “The characters in Israel who keep bringing this stuff up are working against the international interests of the Jewish state.”

That pattern also includes the recent arrests of Conservative women for praying at the Western Wall with a Torah scroll and the kingmaker status of small Orthodox parties in creating and sustaining governing coalitions in Jerusalem.

The smoldering reaction in this country may be changing the character of the pro-Israel movement as secular, Reform and Conservative Jews are turned off, replaced in the activist ranks by Orthodox Jews and growing numbers of Evangelical Christians, whose views on Middle East politics are skewed to the right of the American Jewish mainstream.

Nobody is predicting that the religious wars raging in Israel, and their impact on an American Jewish community that is about 85 percent non-Orthodox, will lead to a precipitous decline in the virtually wall-to-wall support for Israel in Congress and the executive branch.

It’s the potential cumulative impact of the religious wars in Israel, and how it changes the nature of the pro-Israel movement here, that has some Jewish leaders and top-rank politicians worried.

“Support for Israel remains very strong on Capitol Hill,” said Rabbi David Saperstein, director of the Religious Action Center of Reform Judaism. Rabbi Saperstein was in Israel this week with a delegation of top Reform, Conservative and progressive leaders urging defeat of the conversion bill.

But Rabbi Saperstein described a crisis of confidence that could ultimately make pro-Israel advocacy in Washington more difficult, as well as divide American along religious lines.

“Among people who are already committed to working actively to support Israel, it creates disappointment and resentment, but doesn’t lead them to withdraw that engagement and support,” he said. “Among the larger number of Jews who are not as directly involved as activists, or the unaffiliated who identify with the Reform and Conservative movements, the message that the government … does not recognize their commitment does alienate people, and it does make our pro-Israel efforts more difficult.”

While most analysts say the law proposed by Knesset member David Rotem of the Yisrael Beiteinu party won’t immediately change the status of converts to Judaism in the Jewish state, there is widespread anxiety in non-Orthodox circles that the measure, which codifies the Orthodox rabbinate’s monopoly on conversions in Israel, will reinforce the impression that Reform and Conservative Jews are being delegitimized in the Jewish state.

Jewish leaders here, already alarmed by the drift away from Zionist commitment among the young, reacted with barely contained fury.

Jerry Silverman, president and CEO of the Jewish Federations of North America, wrote a letter to Netanyahu expressing “deep shock” that the legislation was moving through Knesset; Jewish Agency Chair Natan Sharansky said, “We cannot divide the Jewish people with legislation which many in the Jewish world view as defining them as second-class Jews.”

In a letter to colleagues this week, Silverman wrote, “The Jewish Federations movement represents all of North American Jewry, including the vast majority — some 85 percent — who could be negatively impacted by passage of this bill. Therefore we stand at the forefront of efforts to prevent this potential rift in our community.”

The proposed law also sparked an outcry from Capitol Hill, where several prominent Jewish lawmakers spoke out forcefully.

As first reported in the Jerusalem Post, Sen. Ron Wyden (D-Ore.) sent a letter to Israeli ambassador Michael Oren outlining his concerns, and Sen. Carl Levin (D-Mich.) told the Post he was “troubled” by the proposal.

The issue dominated a Thursday meeting between Oren and Jewish House members, according to several reports.

“People worry about this because of its political impact, but you have to realize that almost all Jewish House and Senate members are Reform and Conservative Jews,” said a congressional source who asked not to be named. “For many, they’re concerned because constituents are concerned, but also because it affects them personally.”

Even if the Rotem legislation is shelved or modified, as expected, some lawmakers see a broader pattern that could impact Jewish unity and the pro-Israel lobbying effort.

“One of my real concerns is that this is not a new issue,” Rep. Nita Lowey (D-Westchester) told The Jewish Week. “We’ve raised objections to this kind of proposal for as far back as I can remember, because it affects the character of Israel and it affects Jews around the world.”

Lowey isn’t just any member; she’s one of the strongest pro-Israel voices in the House and generally reluctant to criticize Israel’s actions, but she said this is an issue that is “causing tremendous anxiety” among her constituents and her Jewish colleagues on Capitol Hill.

“I expressed my concern to Ambassador Oren and I left a message for Bibi Netanyahu,” she said. “I am extremely concerned. I don’t think there’s any issue that is of such great concern to American Jews as ‘who is a Jew.’ I have asked them to oppose this legislation.”

Tom Dine, the former AIPAC chief, said that the pro-Israel lobby was built on a foundation of secular, Reform and Conservative Jews; efforts in Israel to expand the powers of the Orthodox rabbinate, and the perception that non-Orthodox Jews are being effectively written out of the Jewish state’s future, “blows a hole in the soul” of the pro-Israel movement, he said.

Daniel Sokatch, executive director of the New Israel Fund, said Israeli leaders cannot afford to write off the non-Orthodox majority of American Jews just to suit domestic political needs.

“For years they’ve been paying lip service to American Jewish liberalism, and insisting that liberalism be checked at the door when it comes to Israel,” he said. “So what’s coming through that door are the Orthodox, the hardliners and the Evangelicals.”

The Evangelical component of the shift was apparent at this week’s Washington summit of Christians United for Israel, the group created by Pastor John Hagee that has become an increasingly prominent player in the pro-Israel coalition.

The mainstream Jews who once made up the core of the pro-Israel effort are turned off not just by recurrent “who is a Jew” controversies, but by the growing “demonization and delegitimization of the human rights sector in Israel,” Sokatch said.

Martin Raffel, assistant executive director of the Jewish Council for Public Affairs (JCPA), agreed that drift and disaffiliation are eroding the pro-Israel base, but said it has more to do with a “natural evolution” based on the passage of time.

“The most significant factor is probably generational change,” he said. “The World War II generation established its link to Israel through the Holocaust and the creation of Israel; the baby boom generation responded to the Six-Day War and the Yom Kippur War by seeing Israel’s vulnerability.”

But younger Jews, he said, see Israel through the lens of “two intifadas, two wars in Lebanon. They see a very complex situation that’s no longer black and white.”

As that drift takes place, he said, it is only natural that Orthodox Jews — with their strong religious commitment to the Jewish state and, often, with networks of friends and relatives living in Israel — play a more dominant role in pro-Israel activism.

But recurrent pluralism crises that give many American Jews the sense that Israel does not regard them as real Jews “has the potential to exacerbate these centrifugal forces,” Raffel said. “If the message is that some forms of Judaism are more valued than others, it will have a very hurtful impact.”

Brandeis University historian Jonathan Sarna said that religious leaders in the Jewish state have a legitimate interest in “exerting their power to decide who is a Jew in a state that is seen as being the very center of the Jewish people.”

But politically, “it’s self-evident that if we have a significant number of American Jews who consider themselves Jews, who are considered Jews by their [religious] movements, but are not considered Jews by the State of Israel, it’s going to be harder and harder to ask those people to work to support Israel. I’ve heard people say, ‘If the state doesn’t recognize me, why should I work to support it?’ And we’re not talking about small numbers here.”