American Jewish leaders, reassured by recent indications that Israel won't make controversial changes in its Law of Return, are breathing a tentative sigh of relief as Hannukkah begins.> Jews are preparing to celebrate the beginning of Hanukkah Saturday night. Theobservance, an eight-day commemoration of religious freedom, ends Dec. 10.For many, the proposed change in the definition of who is a Jew is seen as a threat to that freedom and to the unity of Jews worldwide.

"We're not out of the woods by any means, but I have a sense that the law won't be changed," said Rabbi James Rudin of the American Jewish Committee, which sent a delegation to lobby Prime Minister Yitzhak Shamir.

Under current Israeli law, all Jews - defined as the children of a Jewish woman, or converts - are accepted automatically as Israeli citizens.

After the recent Israeli elections, however, Shamir promised the Orthodox religious political parties that he would help pass new legislation to deny automatic citizenship to non-Orthodox converts.

The promise was the price Israel's religious parties demanded for their support of Shamir's Likud party. The religious parties won only 18 seats in the 120-seat Knesset, but the election gave them enough votes to give either the Likud orLabor blocs the majority.

Though changes in the Law of Return would affect only a handful of immigrants each year, the symbolic impact is considerable. It questions the legitimacy of the Reform and Conservative branches of Judaism, to which the majority of Jews, including those in Israel, belong.

Twenty-seven organizations - among them the American Jewish Congress, the American Jewish Committee, B'nai B'rith, Hadassah and all major Reform and Conservative governing bodies - issued a statement Nov. 12 warning of the "enormous damage, actual and symbolic" to Jews living outside of Israel.