A controversial "Who is a Jew" law is trapping Prime Minister Yitzhak Shamir between the demands of religious parties that can keep him in power and Israel's friends in the United States.

Shamir promised ultra-Orthodox parties after a general election on Nov. 1 to back an amendment to Israeli law limiting who can call himself a Jew.Their support gave his rightist Likud bloc a parliamentary majority to form a new government.

The proposed law would grant automatic Israeli citizenship only to those born of a Jewish mother or converted to Judaism by Orthodox rabbis. It would deny citizenship to tens of thousands of Americans converted by non-Orthodox rabbis.

Jerusalem Mayor Teddy Kollek, returning from a visit to the United States, said Monday that Israel risked alienating American Jews and U.S. government support, which totals over $3 billion a year.

"If no one is really fighting for Israel, it is not certain that the support we receive will remain on the same level," Kollek said.

Most of the United States' 5.5 million Jews - the largest Jewish community in the world - belong to the less strict Reform and Conservative movements. Israeli Jews number 3.7 million.

U.S. Jewish leaders are due to lobby Shamir on Tuesday against the bill.

Although Shamir has pledged to stand by his promise to ultra-Orthodox groups, he told 700 visiting British Jews on Monday night, "The state of Israel has no intention to be involved in disputes of all these various religious streams of our people. All are considered part of the Jewish people."

Supporters of the bill argue few people affected by it are trying to move to Israel.

Shamir has urged Labor Party leader and Foreign Minister Shimon Peres to join him in another unity government, but Monday Peres said the chances were slim.

A Labor party source said Peres would not take part so long as Likud rejected his party's demands for two of the top three Cabinet ministries.