Despite Israel's rejection of President Reagan's plan for Middle East peace, the president of a major Jewish organization with branches throughout the world has given his full support for the spirit of the initiative.
The endorsement by Edgar Bronfman, president of the World Jewish Congress based in New York City, seems to indicate that there is considerably more support among Jews around the world for a more flexible Israeli position on Middle East peace than many people realized.
The World Jewish Congress is a kind of parliament of Jewish organizations located in 67 nations.
Mr. Bronfman has also called for an ''immediate and thorough'' investigation into last week's massacre of hundreds of unarmed Palestinian refugees in Beirut while Israeli soldiers were in control of that city. Mr. Bronfman thus placed himself, in effect, behind the unprecedented call for an independent inquiry into the massacre made by Israeli President Yitzhak Novan. Israeli Prime Minister Menachem Begin has turned down Mr. Novan's request.
Bronfman's endorsement of the spirit of the Reagan plan for Middle East peace came in the form of a letter to Mr. Reagan and to Secretary of State George P. Shultz, with whom Bronfman met on Sept. 20.
Israel Singer, executive director of the World Jewish Congress, said that before Bronfman sent the letter the congress polled all 67 Jewish communities. Mr. Singer said the responses to the Reagan plan were mixed, but underlying those responses was a conclusion the plan could constitute ''a major catalyst'' for a solution to the Arab-Israeli conflict.
According to Mr. Singer, an agreement was made with the White House not to make public the text of the Bronfman letter to the President and the secretary of state. But Singer did say that Bronfman qualified his support in one respect. According to Singer, Mr. Bronfman stated that he felt that the entire Reagan initiative was based on the necessity for other parties - and most specifically, Jordan - to enter into negotiations with Israel.
King Hussein of Jordan has said that he sees ''some positive elements'' in the Reagan plan. On Sept. 20 King Hussein called upon the Palestine Liberation Organization to join him in drawing up a plan for a Jordanian-Palestinian federation along lines which would appear to resemble the federation Reagan has proposed.
William P. Clark, Mr. Reagan's national security adviser, said Sept. 21 that King Hussein was ''working hard to gain the endorsement of the Palestinians and other Arabs'' for the Reagan peace initiative.