The Palestine Liberation Organization's main faction, Fatah, today stood firm against allowing Jordan's King Hussein to represent the Palestinians in any talks based on President Reagan's Middle East peace plan. It stressed the "necessity" of convening an Arab summit to adopt a common position opposing the U.S. initiative.

After three days of intensive day-and-night discussions, leaders of the mainstream guerrilla group led by PLO Chairman Yasser Arafat approved a number of "amendments" to a proposed Jordanian-PLO resolution being negotiated between him and King Hussein.

PLO spokesmen would not disclose the content of the amendments but made clear that the organization was not prepared to give the king a mandate to represent its cause in any new American-sponsored negotiations. They said the PLO insisted that the Arab plan adopted in Fez, Morocco, in September is the only acceptable basis for peace negotiations.

The Arab plan reaffirms the PLO as the sole legitimate representative of the Palestinian people and demands the establishment of an independent Palestinian state on land now occupied by Israel.

The Reagan proposals provide no role for the PLO in peace talks, because the United States refuses to deal with the PLO until it recognizes Israel's right to exist. Washington has hoped that the PLO effectively would allow Hussein to bargain on the Palestinians' behalf, possibly by including non-PLO Palestinians in a Jordanian delegation.

The Reagan plan also rules out an independent state, calling instead for a Palestinian entity to be associated with neighboring Jordan.

PLO sources here and in Jordan stressed that the Arafat-Hussein talks have not been broken off, and Arafat's adviser, Khalid Hassan, said that there were "good chances" that the PLO chairman would return to Amman to resume meetings with Hussein.

The Hussein-Arafat talks were suspended abruptly on Tuesday, when Arafat flew here to meet other PLO leaders. Today, Arafat left for South Yemen with the leader of the Marxist Democratic Front for the Liberation of Palestine, Nayef Hawatmeh, apparently biding his time until the king makes known his reaction to the latest PLO move.

The two sides appear to be engaged in hard bargaining in which the lines between public posture and negotiating tactics, and actual progress or lack of progress in the talks, have become blurred. Both sides have been angling to bring Arab and international pressure to bear on the other, and the current confrontation seems to be part of these tactics.

Yasser Abd Rabbo, a PLO executive committee member and spokesman, said there were "many points of differences, basic differences, not minor ones," between the present positions of the PLO and the Jordanian monarch. Both he and another executive committee member, Farouk Kaddoumi, stressed that the PLO would insist on being represented as "a separate delegation" in any American-sponsored peace talks.

The two men are generally regarded as hard-liners within the committee, but Hassan, viewed as a moderate, said virtually the same thing. He denied, however, that the king was actually seeking a mandate in the current talks to represent the PLO, saying that only "cooperation" between two independent delegations was under discussion in Amman.

The king "is in favor of cooperation together, and we are in favor of cooperation together but as two separate entities," he said. "There isn't going to be a Jordanian delegation with non-PLO Palestinian representation."

It has appeared during the discussions here that the PLO has opted for a strategy of using another Arab summit conference to block the Jordanian king from entering the American-sponsored peace talks on the basis of the Reagan plan.

Such a summit is likely only to reassert that the PLO alone represents the Palestinians and to demand an independent Palestinian state, thus making it extremely difficult for Hussein to enter negotiations on the basis of the Reagan plan. Hussein, according to sources in Jordan, has insisted that he will only go to a summit if he already has Arafat's agreement in his pocket.

At the same time, Kaddoumi indicated the PLO will push for an international conference, possibly under United Nations auspices, in which the PLO would participate on the basis of the Arab plan adopted at Fez. But he left open the possibility that the PLO would agree to attend as a part of a larger Arab delegation.