The reported American plan to use United States Marines to supervise the evacuation of Palestine Liberation Organization forces from Beirut is seen as ''a dramatic development'' and ''a considerable risk'' by Israeli officials, according to first reports here.
Israeli sources broke the story to Israel radio before it was released or confirmed in the US, a fact reportedly rousing some suspicion in Beirut.
Israeli sources are stressing that ''all PLO political and military men must leave'' Beirut, an apparent warning that a sweetener to the PLO involving acceptance of its wish to maintain an information office in Beirut will not be acceptable to Israel. Israel radio reported, ''This point may be at the heart of differences between the US and Israel over the next few days.''
Israel radio also reported that official circles say the Israeli Army may agree to withdraw a few kilometers from Beirut if the US sends troops, thus easing the humiliation of pulling out for the PLO.
Israeli officials are likely to be pleased at an American military presence in Lebanon, even if temporary. Israel had wanted US troops to participate in a multinational force to police a 25-mile band of Lebanon above Israel's northern border, an area from which the PLO had been driven.
Arab reaction is not yet fully clear. It is not known whether Lebanon and the PLO accept the plan, but Damascus Radio sharply rejected it.
Egyptian Foreign Minister Kamal Hassan Ali said Tuesday the PLO had accepted a US offer to send military personnel to help Palestinian guerrillas leave London. Ali did not say how he knew of the PLO's approval. His statement contradicted comments by PLO officials in Beirut ridiculing the reported US plan. But Egypt and the PLO have been in regular contact through the organization's representatives in Cairo since Israel launched its military thrust into Lebanon on June 6.