It's up to the Arabs for now.
The Reagan administration is looking for at least qualified support from several key Arab nations in order to generate new pressures for peace on Israel. Direct American pressure on Israel is not called for at this point, State Department officials say.
A State Department Middle East specialist adds that the United States is going to be patient with whatever criticism of the Reagan plan arises from the Middle East at this stage.
''We've got to let everybody get whatever steam they've got out of their systems,'' the official says. ''The important reactions are going to come from Jordan and Saudi Arabia. If they're smart, they'll bite on this.''
But the official adds a note of caution when it comes to the Arab summit meeting now under way in Fez, Morocco: ''We would be amazed to see any clear-cut positive statement coming from there. Whatever comes out is likely to be heavily hedged.''
The theory behind American thinking on the Arab-Israeli peace process - although not openly acknowledged - seems to be this: If Jordan, and perhaps other Arab nations, give the Reagan plan at least qualified support, it will have a positive impact on Israeli public opinion. This might eventually soften Israeli opposition to the plan. The Israeli Labor Party has welcomed the plan.
An irony of the situation is that Yasser Arafat, the chairman of the Palestine Liberation Organization (PLO), now holds strong cards in the closed-door talks going on at Fez. Israel intended to destroy Arafat's movement both militarily and politically. But some Middle East specialists say that while Arafat lost military clout as a result of the Israeli invasion of Lebanon and the PLO evacuation from Beirut, he gained political prestige among the other Arabs.
Michael C. Hudson, director of the Center for Contemporary Arab Studies at Georgetown University, argues that Arafat gained political ''clout,'' because the PLO has now fought longer than other Arabs ever did against the Israelis in previous wars. Arafat no longer has to face the sarcastic comment ''we fought your battles for you'' from the other Arabs, says Mr. Hudson.
''I think it would be difficult for Jordan, Saudi Arabia, or Egypt to get out in front of the PLO on this right now,'' says Hudson. ''But with the PLO leadership now in Tunis, there is a chance that the moderates can move the PLO closer to their thinking.''
Hudson predicts that the PLO will decide on a ''mild rejection'' of Reagan's plan. They'll point out that the plan excludes the possibility of a Palestinian state. But the PLO is likely, he says, to leave the door open to further discussion of Reagan's plan.
One problem for the Arabs in responding to the plan, Hudson says, is that the US is widely believed in the Arab world to have supported the Israeli invasion of Lebanon.
''They will not be quickly convinced that the Americans are operating independently of the Israelis,'' he says. ''And I don't think you will get a real process going on the Arab side of this unless Reagan shows that he is going to stick to his plan and vigorously pursue it despite Israeli opposition.''
The Reagan administration is not totally comfortable with the idea that the PLO still retains considerable clout. But it is certainly not writing the PLO out of the future. Secretary of State George P. Shultz seemed to say recently that the US recognizes that the PLOis part of the Palestinian issue and even plays a representative role in the debate over that issue. On the CBS program ''Face the Nation'' on Sept. 5, Mr. Shultz was asked whether the PLO had been rendered impotent by its retreat from Lebanon or whether it was a force that absolutely had to be dealt with at this moment.
''Well, obviously the Palestinian issue is very much with us and they (the PLO) are seen as part of that issue and standing for it to a certain extent,'' said Shultz. ''I think as a military force, they have been reduced drastically in importance and the support that they were getting from the Russians just was not there.
''And I think also - even more profoundly - that the pattern that they have represented of terror, of violence, as a way of doing something for the Palestinian cause has been shown not to work. And so I would hope that the leaders of the PLO and everyone in the area will start looking at the peace . . . process rather than the violence and the war process.''