King Hussein today broke off a year-long joint effort with the Palestine Liberation Organization to reach a Middle East peace agreement, accusing it and its leader, Yasser Arafat, of breaking their word after Jordan had extracted what Hussein said were key concessions from the United States.

The Jordanian monarch, who has been considered by the United States and Israel to be a key intermediary with the PLO in attempts to reach a comprehensive Middle East peace agreement, announced the collapse of the joint initiative in a 3 1/2-hour televised speech retracing what he called "a grueling year of intensive effort."

Referring to Arafat's behavior this time and in a similarly unsuccessful effort three years ago, Hussein said:

"After two long attempts, I and the government of the Hashemite kingdom of Jordan hereby announce that we are unable to coordinate politically with the PLO leadership until such time as their word becomes their bond, characterized by commitment, credibility and constancy."

"Thus came to an end another chapter in the search for peace," Hussein said, confirming the collapse of the initiative that had been optimistically hailed by all sides after its announcement here by him and Arafat on Feb. 11, 1985. Hussein again endorsed the decision by a summit meeting of the Arab League in Rabat, Morocco, in 1974 that recognized the then-powerful PLO as the "sole legitimate representative of the Palestinian people."

He said that despite its collapse, the joint initiative's "principles and tenets" would "continue to embody the foundations governing relations between the Jordanian and Palestinian peoples with regard to equality of rights and obligations in facing our joint destiny."

Hussein also said that three weeks ago he had rejected a proposal by the United States to join with Palestinians outside the PLO for talks with Israel. "Our unwavering position was no separate settlement," the king said.

But pitching his opening and closing remarks at Palestinians in the West Bank and Gaza Strip, occupied by Israel since 1967, Hussein appeared to be paving the way to staking a claim to represent those Palestinians for the first time in nearly 12 years. The Jordanian parliament is preparing to vote a new election law that would give West Bank residents more representation and, for the first time, enfranchise Palestinians living in Jordanian refugee camps.

Until the collapse of their talks, which became clear when Arafat left here 12 days ago after a final two-week effort to reach agreement had failed, Hussein had refrained from such moves for fear of undercutting their 1985 initiative calling for a confederation between Jordan and the PLO.

As in past peace efforts, that joint initiative failed because of Arafat's refusal to recognize U.N. Security Council Resolutions 242 and 338.

The key resolution -- 242 -- was adopted at the end of the 1967 Arab-Israeli war and stipulated that Israel should return Arab land occupied in the fighting in exchange for being recognized by its Arab neighbors within secure borders.

The PLO bases its rejection on grounds that Resolution 242 speaks of the Palestinian issue only as a refugee problem and makes no mention of a homeland or self-determination for the Palestinians.

Before the crucial final round of talks that began here Jan. 25, Hussein said, his efforts had "borne fruit" in extracting what he called a key U.S. concession. The Reagan administration, he said, agreed that: "When it is clearly on the public record that the PLO has accepted Resolutions 242 and 338, is prepared to negotiate peace with Israel and has renounced terrorism, the United States accepts the fact that an invitation will be issued to the PLO to the international conference."

Acceptance of such a proposed conference in itself represented another U.S. concession. Washington long opposed such a forum because it would allow the Soviet Union to enter the peace process.

Although the Reagan administration sought to limit the scope of any such conference to the largely ceremonial, Hussein said, "The American position had developed to the extent of agreeing to the right of the parties to the conflict to submit any disagreements between them to the conference." But he conceded that Washington had balked at giving the conference binding powers, as Arafat had demanded.

Hussein said he also had persuaded the United States to "go one more step beyond talking to the PLO by accepting to have the PLO invited to the international conference."

Since 1975, U.S. administrations have said they would not consider talking to the PLO until it accepted 242 and renounced terrorism.

Analysts here said they are convinced that had Arafat accepted the plan, on this score at least, the PLO would have driven a large wedge between the United States and Israel.

In fact, Arafat did accept 242 and 338, if only briefly, according to Hussein. He said that last Aug. 15, Arafat and his key advisers, meeting with Jordanian ministers, "reaffirmed his acceptance of all steps and arrangements agreed upon between us, including the PLO's readiness to accept" those resolutions.

But Hussein said he later discovered that Arafat and his PLO Executive Committee, without telling him at the time, had already decided not to accept Resolution 242.

"It has been my destiny to experience the various phases of the Palestine tragedy," Hussein lamented.

He said he now was turning the problem "over to the Palestinian forums in the occupied territories and the diaspora, as well as Arab capitals and organizations."

Where this left Arafat was unclear. But analysts said it appeared that Arafat once again had put the unity of his dwindling troops above risking further splits in the PLO, which has been badly weakened by Syrian backing of member factions that oppose his leadership.

Hussein, freed of his connection with Arafat, Syrian President Hafez Assad's archenemy, now appears to be in a better position to improve his relations with Damascus, the analysts said.

According to these analysts, the only beneficiaries of the collapse of the initiative appeared to be Syria and Israeli hawks intent on solidifying the Jewish state's hold on the occupied territories.