Israel's parliament today turned back a strong attempt to amend the country's basic "law of return" in a manner that critics charged would have had a disastrous effect on Israel's relations with American Jewry.

By a vote of 62 to 51, the parliament defeated the so-called "Who is a Jew" amendment that would have changed Israeli law to recognize only Orthodox conversions to Judaism.

The amendment, which was pushed by the religious parties in Israel's parliament, was opposed by the Labor Party and by a broad coalition of U.S. Jewish organizations that warned that passage of the measure would alienate the vast majority of American Jews who are not Orthodox.

Before the vote, Prime Minister Shimon Peres appealed to legislators not to take what he said would be a divisive step.

"The question of 'who is a Jew' was determined many generations ago," he said. "Our generation is charged with providing an answer as to how to preserve the Jewish people in the face of changing conditions and grave dangers."

The controversy over the issue has existed here for more than a decade and reflects the continuing strains between Israel's religious community, which is dominated by the Orthodox establishment, and secular Israelis. Previous attempts to enact the amendment have failed, but the current push was one of the strongest and there had been predictions that the measure would pass today's preliminary parliamentary test.

The religious parties were supported in today's vote by a majority of the Likud bloc, the main partner with the Labor Party in the national unity government. The Likud has a longstanding alliance with the religious parties that it apparently hoped to preserve by backing the controversial measure.

Following the vote, at least two of the four religious parties scheduled meetings to decide whether to resign from the national unity government over the issue.

Israel's "law of return" grants Israeli citizenship to any Jew who immigrates and asks to become a citizen. It defines a Jew as anyone who is "born of a Jewish mother, or who has converted and is not a member of another faith."

The amendment would have changed the law's section dealing with conversions to recognize only those conducted according to Orthodox rites.

According to Rabbi Richard Hirsch, executive director of the World Union for Progressive Judaism, less than 10 percent of American Jews are Orthodox. The others are Reform or Conservative Jews or have no formal affiliation with any of the three streams within Judaism, he said.

Orthodoxy is the most traditional of the three main branches of Judaism. The Reform movement, begun in the mid-19th century in Germany and highly popular in the United States, shifts away from many traditional practices. The Conservatives straddle a broad middle ground between the other two in religious belief and practice.

Hirsch, who was among those who led the lobbying against the amendment, said passage would have been "a disaster," diverting attention from Israel's major political and economic problems and undermining the traditionally strong support for Israel by U.S. Jews.

"A lot of Jews would have felt that somehow the state had declared them to be second-class citizens," he said.

Israel's state religion is Orthodox Judaism and only Orthodox rabbis are supported by the state and empowered to perform such religious-legal functions as officiating at weddings. Hirsch said Conservative and Reform Jews here "have learned to live with that," but that it would be "another thing completely if the state said that Conservative and Reform Jews are not authentic."

"The significance of this vote," he added, is that the Israeli parliament "has decided that it is not the business of the state to determine the religious practices of Jews abroad."