Prime Minster Menachem Begin of Israel was both surprised and angered when he learned the details of the position which President Reagan of the United States announced and explained last Wednesday on the subject of Palestine.
Both surprise and anger are understandable in terms of the framework within which the President announced his position.
The position followed, as Mr. Reagan said it should, ''the guidelines laid down by my predecessors.'' But it was diametrically opposed to the position which he had expressed during his 1980 election campaign.
The key to the difference between the new Reagan position as stated on Sept. 1 and the campaign position of two years ago lies in the precise wording of a resolution adopted unanimously at the United Nations in New York following the 1967 ''Six-Day War.''
The resolution, known as UN 242, called for withdrawal of Israeli troops from ''occupied territories'' along with peace and independence for every state in the region - in effect requiring Arab recognition of the right of Israel to exist within safe and secure boundaries.
This has been the backbone of the official American position on the subject from the time it was adopted during the presidency of Lyndon Johnson, right through the next three presidencies of Richard Nixon, Gerald Ford, and Jimmy Carter. It is explicitly written into the Camp David treaties and accords. It calls for and expects Israel ultimately to remove its armed forces from those ''occupied territories'' in return for Arab acceptance of the existence of Israel.
The first and only departure by Washington from Resolution 242 has been by candidate Reagan during the 1980 campaign period. In speeches, particularly when addressing Jewish audiences, he referred to Jewish settlements in occupied territories as ''not illegal.''
Previously - throughout Johnson, Nixon, Ford, and Carter presidencies - the planting of Jewish settlements in the ''occupied territories'' was labeled by Washington as being ''illegal,'' was opposed by Washington, and was indeed treated by the Israeli government itself as being illegal or ''unauthorized'' until Mr. Begin became prime minister. Some of the early settlements were in fact dismantled by Israeli troops.
The Jewish settlements in ''occupied territories'' were treated by Washington as being ''illegal'' both under international law and because such settlements would be incompatible with the concept of eventual Israeli withdrawal. There is no point to putting Jewish settlers into those territories if the territories are some day to be handed back to their Arab inhabitants.
When Mr. Reagan called them ''not illegal'' he was by implication abandoning UN 242 and accepting Mr. Begin's intention to claim Israeli sovereignty over the whole of the occupied territories.
It is not clear on the record whether Mr. Begin was given earlier warning that the American President might turn away from his campaign permissiveness toward Israeli territorial expansion and revert to the policies of his four predecessors. But a letter to Mr. Begin, which preceded the Sept. 1 statement by a day, was the first official notice to Israel and to Israeli supporters in America that Mr. Reagan had decided to reenter the area inside ''the broad guidelines laid down by my predecessors.''
This he has now done, fully and firmly.
He called for a freeze on the Jewish settlements in the occupied territories. He proposes immediate progress toward ''free elections for a self-governing Palestinian authority'' by the Arabs.
If these proposals are put into effect the end result will be Israel having to retire substantially into its pre-1967 frontiers and having to give up the Begin intention to bring all the occupied territories under Israeli sovereignty. President Reagan is insisting that Palestine be shared and divided, not ruled in its entirety by Israel.
This puts the President of the US right across the road down which Mr. Begin has been marching. It is total confrontation between the two. The issue is joined in public. It will be waged on the field of American politics. Mr Begin will call his American friends and supporters to a campaign to try once more to outvote the American President in the American Congress.
This will be as hard a test for Mr. Reagan's political skills and determination as the battle over the new tax bill has been.