UN Resolution 242 has been a bone of contention since it was signed. But the conflict flared anew after a top adviser to Ehud Barak said publicly that Israel's prime minister had told his cabinet on Sunday that he believed 242 - and the supporting UN Resolution 338 - has no standing in the West Bank.
Mr Barak added fuel to the fire during a trip to Paris by repeatedly saying that the resolutions mean different things when applied to Palestinians than when referring to Arab nations with recognised borders. They have "a different context," he said.
The issue dominated an appearance at the 21st Socialist International Conference in Paris by Mr Barak and Yasser Arafat, the Palestinian leader, and served as a sobering reminder of how far the two sides have to go to end their conflict.
Resolution 242, signed in 1967, calls for the Israelis to withdraw from land seized in the Six Day War in return for peace and security. Israel believes that it does not apply to the West Bank and Gaza, as they were not recognised as part of any state before Israel occupied them. Their status was in limbo after the 1948 UN recommendation that Palestine be split into Jewish and Arab states; after the ensuing war, Gaza was taken by Egypt and the West Bank by Jordan.)
Mr Barak's pronouncements have irritated the US and run contrary to his efforts to portray himself abroad as a concession-making peace-maker. It is not a new Israeli position; Mr Barak has made clear that Israel does not intend to withdraw to the 1967 borders and has granted more tenders for Jewish building on the West Bank than his right-wing predecessor, Benjamin Netanyahu. But the timing is sensitive. It comes as both sides - nudged on by Bill Clinton - have just opened direct talks on a framework for a final settlement next year.
Mr Arafat pounced on the disagreement in a speech to the Paris conference yesterday. He entered the hall to a standing ovation, walking shoulder- to-shoulder with his Israeli adversary. But he soon went on the attack, with a pointed comparison between Mr Barak and Yitzhak Rabin, the premier's friend and mentor.
Mr Rabin, said the Palestinian leader, "accepted a compromise solution based on international legality and embodied in United Nations Security Council resolutions 242 and 338, which call upon Israel to withdraw from the Palestinian territories occupied in 1967 in return for peace and security."
Although the two leaders made some conciliatory noises yesterday, they seemed to fall out anew in an exchange over the Latrun pocket, a strategic area on the West Bank between Tel Aviv and Jerusalem. The Palestinians have listed it as an area that Israel must not annex. But Mr Barak said that, though never annexed, it was part of Israel nonetheless.
Every coma counts in these arguments. Take the text of Resolution 242 itself. Israel believes the English version, drafted by Lord Caradon when he was British ambassador to the UN, is definitive because it refers only to "territories". The French version, which calls for withdrawal from "the territory" is preferred by the Arabs. Sometimes hopes of reaching an agreement by next September seem wildly optimistic.