Palestine Liberation Organization Chairman Yasser Arafat and Jordan's King Hussein appeared today to be nearing agreement on a formula that would enable the king to respond positively to President Reagan's Middle East peace initiative.

The indications were, however, that the arrangement would not be announced publicly until after it received the blessings of Arab states at a summit meeting in Morocco later this month, possibly April 16 or 17.

The developments followed a frenzied day here in which Arafat and Hussein sought to resolve what were described as minor differences in the language of a draft joint communique they worked on today.

Arafat also convened here the first full-fledged session of the PLO's executive committee to meet in Jordan since the group was banished during the Black September battles between the PLO and Jordanian troops here in 1970. For several members of the PLO's pro-Libyan and pro-Syrian factions, it was their first visit to Amman in 13 years.

Despite the newly optimistic mood around the talks, western and Arab diplomats cautioned that the effort to reach agreement could still fail as the bargaining over final details continued. Moreover, they warned that going to a summit represented a calculated risk for Hussein and his moderate Arab supporters, who can expect to see a renewal of strong pressure from Libya and Syria on the radical Palestinian groups within the PLO.

The executive committee apparently did not give Arafat any strong endorsement to go ahead with the peace negotiations. But, at the same time, it did not reject the Reagan plan outright nor did it block Arafat from cutting a deal with Hussein.

Moreover, even the most radical members of the committee, complaining of the failure of the Reagan plan to approve the idea of an independent Palestinian state and to recognize the PLO as the sole representative of Palestinians, went to great lengths to stress the organization's good relations with Jordan.

According to diplomats here and advisers to Hussein, the king feels that it is essential for him to have Arafat's backing to begin negotiations for the creation of a Palestinian entity in the West Bank and the Gaza Strip that would be linked to Jordan as envisioned in the Reagan plan. He and Arafat have held four meetings during the past three days to discuss the initiative, and there were indications that they may meet again Tuesday.

There were reports that Saudi Arabia had played a strong behind-the-scenes role in gaining Arafat's agreement to come to terms with Hussein and that the Saudis were behind the moves for an Arab summit to endorse the arrangement.

According to the reports, the Saudis got Arafat's commitment in February but the PLO chairman chose to delay his meetings with Hussein until after he touched base with the disparate factions within his organization, especially the representatives of the hard-line pro-Syrian and pro-Libyan groups.

Arafat delayed his visit here for four days, taking a winding detour to Saudi Arabia where he held the latest of several sessions with King Fahd, then went to Iraq, Kuwait, Bahrain and Syria, where he conferred again with radical factions before coming here to meet the king.

There were still indications here today that the pro-Libyan and pro-Syrian factions were creating some obstacles, but they did not appear to have shut the door on possible future negotiations.

Shortly after noon an aide to Arafat flashed a copy of what he described as a four-page joint communique Hussein and Arafat had drafted, and he said that it would be released publicly later in the afternoon.

He read portions of the draft that seemed to indicate that the king and Arafat were attempting to find some bridge between the Reagan plan and the Arab League's Fez declaration, drawn up at the last Arab summit in Fez, Morocco, last September and calling for an independent Palestinian state and recognition of the PLO as sole representative of the Palestinians.

"It's a good agreement," said the aide, Imad Shakour, Arafat's adviser on Israel. "Those who think relations between Jordan and the Palestinians are troubled are mistaken."

But later in the day, after the executive committee held the second of two meetings, PLO aides said the communique would not be made public today and indicated that it might not be fully disclosed until after the Arab summit. The PLO sources said vaguely that the problems had come not from the Jordanians but from the PLO side, apparently referring to the executive committee. There were strong indications that the pro-Syrian faction had raised the obstacles.

The state-run Damascus radio announced this evening that Syrian President Hafez Assad and George Habash, leader of one of the pro-Syrian factions, met today in Damascus to discuss "the need to confront the Zionist imperialist conspiracy aimed at liquidating the Palestinian cause and imposing a capitulating settlement at the expense of the Palestinian peoples' inalienable rights."

But there was hope among some Arab diplomats here that even the Syrians would eventually agree to participate in the Morocco summit.

An Arab diplomat watching the unfolding of negotiations between Arafat and Hussein said he believed that the difficulties had stemmed from the PLO's desire to be recognized by the United States and not be cut out of peace negotiations.

"They have lots of doubts about what the Israelis will do," he added, "and how far the U.S. will be willing to go."

Those sentiments were reflected this evening by a PLO source who briefed reporters on the outcome of today's events.

"While the PLO is giving hints and signals for a political settlement, the Israelis are building more colonies and settlements on the West Bank," he said. "That means there is no confidence on our side on the American-Israeli positions."

There were hints here that PLO members were impressed by Reagan's announcement last week that he had delayed the sale of F16 planes to Israel because of its failure to withdraw from Lebanon, but PLO members indicated strongly that they were seeking firmer commitments and assurances from the United States to get the Israelis to withdraw from the West Bank and Gaza.

But clearly the meetings here during the past few days have taken place against the backdrop of a sense of urgency that failure to act now could mean that the PLO dream of an independent state was irrevocably lost.