In the swirl of bluff and rumor surrounding key talks here between Jordan's King Hussein and Palestinian leader Yasser Arafat, one development has emerged clearly: the king has proved to be a tough bargainer in seeking a firm mandate from Arafat to enter negotiations under the auspices of President Reagan's Middle East peace plan.

The consultations have been held in extreme secrecy, and it is impossible for those outside the small circle of informed persons to separate fact from negotiating tactic and from self-serving rumors. Some versions of the talks' contents, however, have been leaked in reports from Kuwait and Syria quoting Palestine Liberation Organization leaders.

According to these accounts, the king threatened to enter peace negotiations alone if Arafat refused to allow him to bargain on behalf of the Palestinians.

Hussein also allegedly told Arafat that he would hold a referendum in Jordan and among Palestinians on the West Bank to gain support for such a move. If successful, such a vote effectively would undermine the PLO's claim to be the Palestinians' sole legitimate representative.

Hussein's threats came as he pressured Arafat, the PLO's chairman, to sign a joint communique allowing the king to respond positively to Reagan's Sept. 1 plan. Arafat reportedly agreed orally but balked at putting it in writing.

According to a report from Damascus quoting an unidentified senior member of the PLO executive committee, the proposed joint communique said in part: "Taking into consideration that President Reagan's initiative, which is based on U.N. Resolutions 242 and 338, recognizes the legitimate rights of the Palestinian people, the two parties resolve to enter negotiations."

There were indications here, however, that the language of the proposed communique was less stark. It was possible that the PLO's pro-Syrian faction was trying to embarrass Arafat by floating reports that he was considering embracing the Reagan plan so closely.

Arafat on Tuesday abruptly called a recess after three days of talks with the king and flew to Kuwait to consult with other PLO leaders in lengthy, secret meetings. Available reports indicated that the chairman was coming under very heavy pressure from militant colleagues to resist a deal.

The feeling here, as one well-informed diplomat said, is that "Arafat is not going to come through easily or cleanly because that isn't the PLO mood."

PLO spokesman Yasser Abd Rabbo and Arafat's second-in-command Salah Khalaf said in Kuwait early Friday that PLO leaders have refused to authorize Hussein to negotiate on behalf of the Palestinians, Reuter reported. Rabbo added, however, that talks would continue later Friday.

Reagan's plan calls for Palestinian self-government in an entity to be created on the West Bank and Gaza Strip, which now are occupied by Israel. The entity would be associated with Jordan, which controlled the West Bank before the 1967 Middle East war.

Radical factions in the PLO want any talks to fall under the framework of the Arab League's plan formulated at the summit in Fez, Morocco, several days after Reagan announced his initiative. The Fez formula calls for creation of an independent Palestinian state under PLO leadership.

Interestingly, Arafat himself was cited as a source of reports of Hussein's threats to enter talks on his own or to call a referendum if the PLO did not cooperate. This suggests that the wily PLO leader may be revealing the threats to apply pressure on PLO rejectionist factions.

In public comments, Jordanian government officials here denied that the king had delivered such warnings. They suggested that the reports were part of a "disinformation campaign" being waged by PLO radicals.

But other sources recalled that Hussein in 1979 had told Nicholas Veliotes, former U.S. ambassador to Jordan and now assistant secretary of state for Near Eastern and South Asian affairs, that he believed he could win the support of West Bank Palestinians in a plebiscite.

According to sources here, Hussein presented Arafat with a list of topics to be discussed here when the two were at the summit of the Nonaligned Movement in New Delhi last month. It was a tactic designed to pin down the PLO leader on specifics and avoid vague responses, the sources said.

Moderate advisers to Arafat thought that he had agreed to sign a communique on Monday and waved copies before reporters of what they described as a handwritten four-page draft. They said then that the communique would be released Monday evening.

But those plans clearly hit a snag, which remains unexplained, after Arafat presented the draft to members of the PLO's executive committee meeting here. The communique was not released, and, moreover, rejectionist pro-Syrian members of the executive committee emerged from that meeting with strong rhetorical blasts against the Reagan plan.

In Kuwait, one Palestinian source said that Arafat's second-in-command Khalaf, also known as Abu Iyad, was dead set against approving Hussein's entry into talks. PLO spokesman Rabbo denied reports that Hussein had given the PLO 48 hours to say yes or no.

There is a view here that West Bank residents are eager for movement toward negotiations because of growing anxiety over Jewish settlements and restrictive policies of the occupation forces there. The view is that the PLO could lose support if it is seen as trying to prevent talks.