The extraordinary summit meeting scheduled for next week in Casablanca, Morocco, could make or break the slow-moving Middle East peace initiative put forward by Jordan's King Hussein and the Palestine Liberation Organization, according to Jordanian and Palestinian officials.

Although Jordan was the first country to accept the renewed call last Saturday for a summit by Morocco's King Hassan II, Jordanian officials say privately that they never have gone into such a meeting with more uncertainty about what they will get out of it.

PLO officials talk of the summit openly as a challenge to Syria -- which opposes the Jordanian-Palestinian plan -- and say they expect violent moves by Damascus in the next few days in an attempt to thwart it.

Despite the mounting obstacles to success at the summit, the Jordanians are hoping for a broad endorsement of the joint peace initiative. To do this in the context of what King Hussein has termed a new "constructive alliance" among the more moderate Arab states obviously would be a major breakthrough in the peace process.

Yet even some Jordanian officials wonder privately if isolating Syria and angering it is going to help the peace process in the long run. The original idea for a summit was promoted this spring by the PLO to protest the Syrian-backed war on Palestinian refugee camps in Lebanon. So whether Syria attends or not, it is likely to find itself isolated and criticized by many of the Arab states it has sought to dominate.

Previous Arab summits have operated on the basis of unanimity, and Syria could tie them up or prevent them from taking place by withholding its approval.

"This conference will strengthen the majority's power to make decisions," said Khalil Wazir, deputy commander of the PLO and a cofounder of Fatah with Arafat, in an interview here. "This is what we are stressing with most of the Arabs who are fed up."

Even among nations friendly to the idea of the summit, however, the joint Jordanian-PLO peace initiative faces heavy opposition.

At a press conference in Morocco Saturday, Hassan suggested that the Palestinian question as a whole would be examined in light of the peace plan forged at the last Arab summit in Fez, Morocco, in 1982.

"If these Jordanian-Palestinian initiatives are compatible with the Fez plan, the summit can only approve them," Hassan said. "In the contrary case, the summit will invite the Jordanians and Palestinians to modify their action or abandon their initiative."

The key to the initiative's survival thus far has been the ambiguity of central passages in the joint Jordanian-PLO accord signed Feb. 11, especially regarding the creation of an independent Palestinian state.

The United States and Israel flatly oppose an independent Palestinian state of any kind.

The Fez plan called unequivocally for "the establishment of an independent Palestinian state, with Jerusalem as its capital."

The February accord talks more vaguely of a confederated Jordanian and Palestinian state and thus was able to sidestep some of Washington's objections.

The Jordanians are reluctant to let the delicate wording of the initiative be put to the Fez test.

After Hassan's announcement both Palestinian and Jordanian spokesmen were quick to say that they consider the Feb. 11 accord a bilateral agreement and will not submit it for debate or modification.

Wazir said tonight, however, that the PLO is ready to defend the accord as it is, maintaining that it is a logical outgrowth of Fez.

"We are confident in defending it," said Wazir, who is also known as Abu Jihad. "We are breaking through the wall with this, and we are going ahead with this."

Yet many Palestinians express increasing frustration with the initiatives, which seem to have ground to a halt.

A planned meeting between a joint Jordanian-Palestinian delegation and U.S. Assistant Secretary of State Richard W. Murphy, portrayed here as a vital step in the process, has been stalled for weeks now as the PLO makes it clear that it wants to find itself at the negotiating table soon, and as Washington makes it clear that this is unacceptable.

Mohammed Milhelm, a prominent member of the PLO executive committee and a former West Bank mayor who once met with Secretary of State George P. Shultz in Washington, talked with open sarcasm this week about the prospects for the Murphy meeting.

"They may give us the honor of talking to us to tell us one very short statement: 'Go and talk to Israeli Prime Minister Shimon Peres,' " said Milhelm. "Then they will be kind enough to be there as witnesses that Peres will not give us anything, and they will shrug their shoulders and say, 'Sorry, there is nothing we can do.' "

In this atmosphere of frustration and uncertainty, some Jordanians say they are worried that once the summit begins, the PLO could embrace modifications and clarifications to the Feb. 11 accord as a way to end the current process.

But Wazir dismissed this concern. "If the United States comes around, okay," he said. "If not, we have experience with patience."