NEW YORK (AP) _ Many American Jews are thinking twice about giving money to Israel because of a growing assertiveness by Orthodox groups over the question of who is a Jew.

Reform and Conservative rabbis are asking constituents to send a message with their checkbooks. Liberal and apolitical Jewish charities are getting more donations than ever before. And traditional conduits for Jewish philanthropy _ like the United Jewish Appeal, which finances social services regardless of religious affiliation _ are hearing from donors who don't want their dollars going to anything with Orthodox ties.

One beneficiary of this trend has been the New Israel Fund, which supports civil rights groups, battered women's shelters, environmental activism and even burial grounds for non-Orthodox Jews in Israel.

``Several people have told us that they're shifting their gifts ... in order to send a message that they are unhappy about the very heavy influence that the ultra-Orthodox are having in Israeli political life,'' said Gil Kulick, spokesman for the New Israel Fund. The organization raised $13 million last year, 20 percent more than the year before.

``I am absolutely dedicated to switching my contribution because I feel the New Israel Fund is funding things I believe in,'' said Virginia Greenwald of Pittsburgh, who in past years donated stock to her local UJA federation. ``I'm very deeply concerned about what's going on in Israel.''

Ninety percent of U.S. Jews are Reform and Conservative, and many of them, like Ms. Greenwald, are infuriated by the rise of the right in Israel. The peace process has slowed, legislation is pending that would invalidate non-Orthodox conversions, and some ultra-Orthodox groups are rejecting the legitimacy of other branches of Judaism.

Last month, the titular head of the Conservative movement in America, Rabbi Ismar Schorsch, issued a call to arms, saying there should be ``no more contributions to people who privately treat our religious beliefs with disdain and derision.''

``Religious pluralism has to be elevated as a top priority,'' Schorsch, chancellor of the Jewish Theological Seminary, added in an interview. ``Otherwise the state of Israel is going to end up not as a Jewish state but as an Orthodox one.''

Schorsch would like the UJA to take a stand too, but spokesman Bernie Moscovitz said the organization could never make it a rule to help ``a poor kid as long as they're not ultra-Orthodox.''

The Jewish Federation of Greater San Jose, the UJA's regional fund-raising group in Silicon Valley, recently adopted a policy under which donors can designate their gifts for groups that support religious pluralism and Jewish-Arab coexistence.

``There are a significant number of people in our community who are extremely concerned,'' said spokesman Jon Friedenberg. ``Many of them have been very pleased that their federation has a mechanism to allow them to speak as a community rather than as individuals.''

David Landau, an influential Orthodox columnist for the Israeli newspaper Ha'aretz, castigated Schorsch's demands as ``bald threats of extortion.''

It remains to be seen whether it will have a big financial impact. New Israel Fund's $13 million a year and the $50,000 that the San Jose UJA hopes to put towards pluralism are small compared to the $300 million a year sent overseas by the UJA. Moscovitz says there is no evidence of any large-scale drop-off in donations.

Also saying they are unaffected are the Lubavitchers, an ultra-Orthodox group whose outreach to less observant Jews draws financial support from Conservative and Reform donors.

Since Zionism's early days, Israeli Jews have counted on cash from Jews in the United States and elsewhere to help pay for economic development, social services and military endeavors. Currently, between $500 million and $1 billion a year is donated annually by U.S. Jews to Israeli charities.

Some of these charities remain outside the debate over Orthodox influence.

``The political climate in Israel has very little to do with our fund raising,'' said Maureen Schulman of Haddassah, which raises $87 million a year in the United States for medical care in Israel.

Tel Aviv University, Hebrew University and the Israel Institute of Technology all say their U.S. fund raising is up; the three now raise roughly $120 million a year here.

The reason, says Susan Leader of the American Friends for Hebrew University, is simple: ``We are apolitical.''