Post '48? Now we're looking at a massive humanitarian crisis as the Arabs push the Israelis to the sea, and if it's in the '60s or later that means nukes flying. Here, the US accepts the refugees, then depending on how hawkish and pro-Israel the regime is, every major city in the Middle East glows in the dark, anyone insufficiently Jewish is purged from Palestine, and the US moves the Israelis back in as the defenders of FREEDOM (tm) or something idiotic like that. Then the US undergoes a political crisis in the fallout.
US wasn't massively pro-Israel until 1973 and when the US became that say goodbye to any chance of the Arabs winning. An idea I've thought of if Lehi's plot to kill Truman in 1947 worked, making Secretary of State George Marshall become president. Marshall was pro-Arab, so he could probably make US foreign policy support the Arabs. Alongside that the Israeli right was weak until the 1970s, so Israel might become pro-Soviet. Wonder what the pro-Arab US and Zionist USSR does in an Arab victory scenario in the conflict as you've mentioned.