JERUSALEM — Key American Jewish organizations have pledged to support a campaign against new legislation that would bar official state recognition of Conservative and Reform conversions performed in Israel.

Some believe the issue could turn into a repeat of the vitriolic "Who is a Jew" controversy that plagued Israeli-diaspora relations half a decade ago.

The conversion issue, always politically sensitive in Israel, surfaced in its current form after a recent decision by the High Court of Justice that opened the way to state recognition of Conservative and Reform conversions performed in Israel.

Orthodox leaders viewed the court decision as diminishing their control over major life-cycle events, including marriages, in the Jewish state.

Meanwhile, non-Orthodox and secular groups in Israel are campaigning against the proposed legislation, which has been demanded by the Orthodox parties.

Hillel Shuval, chairman of Hemdat, an Israeli lobbying group for religious freedom and pluralism, said representatives of the American Jewish Committee, the American Jewish Congress, the Anti-Defamation League and leaders of the Conservative and Reform movements will ask Prime Minister Shimon Peres and other ministers to quash the legislation.

Members of these American Jewish groups are planning to be in Israel next week to attend ceremonies marking the end of the 30-day mourning period for slain Prime Minister Yitzhak Rabin.

On Monday, Israeli representatives of these American Jewish movements, together with leaders of pro-pluralism Israeli movements, met at the Knesset with sympathetic members of the Labor, Meretz and Tsomet parties to form a coalition against the proposed legislation.

Shuval said the Labor Party is split on the issue, with several Knesset members likely to balk at any party requirement to endorse the legislation.

The Israeli groups opposed to the legislation include the Masorti movement, Israel's Conservative movement; the World Union of Progressive Judaism, with which the Reform movement is connected; Na'amat, the Histadrut's women's movement; the Israel Women's Network; the Association of Civil Rights in Israel; and Yisrael Hofshi, a new movement representing immigrants from the former Soviet Union.

Non-Orthodox conversions performed abroad are already recognized in Israel.

All of the Orthodox parties immediately reacted to the court ruling by demanding that the Knesset pass legislation barring the recognition of non-Orthodox conversions. The Knesset has the right to pass legislation overturning a court decision.

The Orthodox parties found themselves fighting an uphill battle when they stood in solid opposition to the coalition of Rabin's Labor Party and its secularist partner, Meretz.

But the Nov. 4 assassination of Rabin and the subsequent political shifts have brought the Orthodox parties back into the very heart of coalition politics.

In the week since Peres' new government assumed power, Labor ministers have been conducting vigorous negotiations with the National Religious Party and with the three fervently Orthodox parties, Shas, Agudat Yisrael and Degel HaTorah.

On Monday, Peres promised the two chief rabbis, Yisrael Meir Lau and Eliyahu Bakshi-Doron, that a Cabinet committee under the minister of justice would be established to seek acceptable solutions to the problem.

Peres had wanted to create the committee at this week's Cabinet meeting, but postponed the plan after confronting stiff opposition from its dovish coalition partner, Meretz.

The Orthodox parties contend that the High Court decision changed the status quo on matters of state and religion, whereas the Rabin government had pledged in 1992 to uphold the status quo.

The Orthodox parties, mindful of the major Israeli-diaspora crisis generated over an earlier version of the conversion question in 1989, claim that the current version is a purely internal matter, because it concerns conversions performed on Israeli soil.

In the 1989 episode, which exploded into the infamous "Who is a Jew" debate, the Orthodox parties sought — unsuccessfully — to enact legislation that disqualified anyone who had been converted abroad by a non-Orthodox rabbi to immigrate to Israel under the Law of Return.

At that time, many American Jewish organizations conducted an unprecedented lobbying effort to pressure both Labor and Likud to forgo the proposed legislation.

For their part, the American Jewish groups firmly reject the Orthodox attempt to draw a distinction between conversions performed abroad and those performed in Israel.

"To us — this is `Who is a Jew' through the back door," said Shuval, who is flying to the United States this week as part of an Israeli delegation seeking to generate support for the pluralist position.