A summit meeting of moderate Arab leaders ended today by declining to endorse a joint Jordanian-Palestinian peace initiative that its proponents called "the last feasible chance" for peace in the Middle East.

But several senior Arab officials said in interviews that the summit's final communique, released this afternoon, intended to leave the door open for Washington to make the next move toward Jordan and the Palestine Liberation Organization.

The Jordan-PLO initiative is regarded by U.S. officials as the most positive new development in three years in the long-stalled Middle East peace process. Designed carefully to take into account Washington's criteria for movement toward Israeli-Arab talks, it nevertheless has floundered in recent months on the question of precisely who would take part in any preliminary dialogue.

U.S. officials as well as the Jordanians and the PLO had expressed hopes that the emergency summit here would give the process new momentum and energy. These hopes were encouraged by the absence here of the most intransigent Arab states.

But when the final communique was read in the opulent Casablanca palace of King Hassan II, it began to be clear that the Arabs -- even the most moderate by Washington's standards -- are waiting impatiently to see Washington's next move.

"We want first to know if this agreement between the Palestinians and Jordanians is going to work or not," Oman's foreign minister, Youssef Alawi, said late yesterday when the communique was taking shape.

Other Arab officials who spoke today on condition that they not be named reiterated their feeling that the joint accord signed by Jordan's King Hussein and PLO Chairman Yasser Arafat on Feb. 11 had shown no progress.

"We don't know what they are doing now," said a senior Moroccan official. "There is no joint delegation. The Americans have not agreed to meet a delegation. There is no American-Jordanian-Palestinian dialogue. Just what have they done?"

"They can proceed," said the Moroccan. "We don't say, 'You don't have the right to do what you are doing,' but we can't endorse it because we don't know where it is going."

One influential Palestinian reflected similar disappointment in the accord but not in the summit.

"The accord was created and specifically addressed to the United States. And they didn't buy it," the Palestinian said. "We created a commodity that has no market."

But the official added that he thinks the summit communique "is a message to Washington."

A month ago Jordan and the PLO submitted to the Reagan administration a list of prospective members for a joint delegation to meet with Assistant Secretary of State Richard Murphy. No official response has been received by the Jordanians although there are reports that Washington has asked for more Palestinian names.

"If this meeting with Murphy had taken place before the summit the impact would have been tremendous," said Oman's Alawi. "But because it didn't, you have this."

The debate over the February accords was fierce in the closed meeting, according to participants and reports in the Arab press.

"It was not easy yesterday," said a senior Moroccan official. "We spent all day talking about the Jordanian-Palestinian plan. Of course they wanted an endorsement, but to try to arrange everybody, it's not easy."

The closely supervised Jordanian press quoted King Hussein telling the summit that a retreat from the commitment to the Palestinians -- a reference to the joint initiative -- "could take us back to a state of inaction and paralysis."

"In this joint action lies the last feasible chance to rescue land, people and holy places," Hussein reportedly said. "If it succeeds, well and good. If not, we must be prepared to face the consequences and God help Palestine, its people and all of the region."

Jordanian and Palestinian officials say the king was not looking so much for a specific endorsement as a general vote of approval. Blocked by the Saudis and other states concerned at the absence of Syria, Algeria, Libya, South Yemen and Lebanon, according to Arab officials, the Jordanians and Palestinians were not able to get this.

At the same time, there were fears among some Jordanian officials that the summit might limit the scope of the joint initiative to the peace plan put forth at the last full Arab summit in 1982 in Fez, Morocco. Because the Fez plan calls unequivocally for the establishment of a Palestinian state with Jerusalem as its capital, it is considered unacceptable by Israel and the United States.

The February accord, however, talks of Palestinian confederation with Jordan in terms U.S. officials say may be vague enough to mollify Washington on this point.

The final communique waltzed around this question. It called in general terms for adherence to Fez and specifically cited the need to return all occupied lands and Jerusalem to the Palestinians, but it stopped short of demanding an independent Palestinian state.

All sides at the summit thus were able to say they were content.

Asked if the summit had endorsed the accords, Moroccan Foreign Minister Abdulatif Filali said, "No, no, no. It's not an endorsement. We 'took note.' "

Yet Jordanian Foreign Minister Taher Masri insisted the summit had issued an endorsement that is "not conditional. We're very happy. Read the language."

There was no official English or French translation of the communique. But regarding the Jordan-PLO initiative, the communique said, in unofficial language, that "the summit heard detailed explanations" from Hussein and Arafat about the Amman agreement. "It noted with appreciation their explanation on the harmony between the Jordanian-Palestinian plan of action and the Fez plan.

"After discussing the matter, the summit reiterates the need for unanimous Arab abidance by the spirit and the resolutions of Fez," the communique concluded.