Enthusiasm over the prospects for rapid movement toward a new round of substantive Middle East peace diplomacy has faded among Jordanian officials and Palestinians here following the cautious reception their Feb. 11 initiative has received in the United States and Israel.

Officials close to King Hussein and Chairman Yasser Arafat of the Palestine Liberation Organization say the United States has yet to make the necessary step to match that taken by the Feb. 11 accord.

Tactically, this stance apparently reflects a desire to keep pressure on Washington to meet King Hussein's central demand that the United States confer with a joint Jordanian-PLO delegation about the future of the occupied West Bank.

Jordanian officials interviewed this past week gave the impression that the Reagan administration, recalling its bitter recent experience in Lebanon, is only reluctantly abandoning its "very negative" refusal to get involved directly in Mideast peacemaking.

Some of the U.S. statements, they suggested, seem designed primarily to counteract impressions that Egyptian President Hosni Mubarak had left Washington empty-handed after a visit during which he had accused the administration of "defeatist attitudes."

With such key problems as the makeup of any joint delegation still unsolved, however, any predictions now about the eventual fate of the initiative would be "premature," the officials said.

They noted that Richard W. Murphy, the assistant secretary of state for Middle East affairs, was due to visit the region in mid-April.

Even then, the officials cautioned, no firm results from what the officials called these "exploratory" talks were likely much before King Hussein is expected to visit Washington in May or early June.

What is left is an apparent Jordanian belief that by early summer Israel will have completed its evacuation from Lebanon and that Prime Minister Shimon Peres will have improved his political stature. Perhaps he would decide then to risk a rupture with his coalition partners from the Likud bloc by making a step forward of his own on the peace front.

If the Jordanians are cautious and wary, PLO officials are deeply pessimistic.

Mohammed Milhelm, a former West Bank mayor generally considered a relatively moderate member of the Executive Committee, said his optimism at the time of the February agreement had evaporated to the extent that "I don't think it will produce anything."

"I thought the United States would change perhaps not 180 degrees, but maybe 90 or 100," he said in an interview. "Instead, Washington is paralyzed and is beating around the bush. I feel the United States wants to destroy Arafat and the PLO."

By that he said he meant the February initiative had failed to budge U.S. opposition to an international peace conference and insistence on direct Arab-Israeli negotiations and on explicit acceptance of U.N. Security Council Resolution 242 recognizing Israel's right to exist.

Moreover, Milhelm expressed fears that despite the PLO's current understanding with Jordan, U.S. tactics sought to extract concessions that "will make us lose the confidence of our people" and "violate the resolutions of the Palestine National Council," the PLO's parliament-in-exile.

This problem was underscored by a series of interviews by Mubarak before he left for his recent Washington visit in which he exposed carefully couched ambiguities in the initiative's text or, in the words of one diplomat, "crossed the t's and dotted the i's."

Nonetheless, informed sources insisted that behind-the-scenes discussions aimed at putting together a joint delegation that hopefully will satisfy both the United States and the PLO were about to begin.

As before, such moderate Palestinians as Edward Said, a Columbia University professor of comparative literature, and Walid Khalidi, a Harvard history professor, were mentioned.

Still unclear was whether the PLO could endorse such candidates without formally identifying them as PLO officials. This is a ploy often suggested to bypass U.S. refusal to deal with the PLO unless it recognizes the Jewish state.

Also complicating the task of Jordan and the PLO was the knowledge that their peace initiative is far from universally popular with their own public.

The example of the Shiite Moslem resistance to the Israeli Army in southern Lebanon -- widely viewed here as the first time Arabs have stood up and forced the Israeli military to retreat -- has enhanced the prestige of armed struggle and further embarrassed the king and Arafat.

Arafat supporters are aware of their own inability to match the Shiites' performance in the field, although they raise the specter of mass expulsions of Palestinians if West Bank residents should seek to emulate the southern Lebanese.

King Hussein, whose alliance with Iraq underscores his fears of instability should Shiite Iran win the Persian Gulf war, recently had the Jordanian press play down the southern Lebanon resistance, apparently out of fear of fueling criticism of the February initiative.

Against this backdrop, Syria's President Hafez Assad has reminded Arafat and Hussein of their increasing vulnerability.

In a widely heard major speech broadcast from Damascus earlier this month, Assad denounced the "delusion" that the United States would put pressure on Israel to exchange Arab land occupied in 1967 in return for peace.

Celebrating the fighting in southern Lebanon, Assad asked, "Why should Israel give them Palestinians the land of Palestine when they would neither be a major obstacle if it decided to fight nor achieve peace if it decided to make peace?"