The United States seems to be at another crossroads in the Middle East. King Hussein's refusal to join US-sponsored negotiations on autonomy for the West Bank is a grave disappointment. The President says he remains ''very hopeful'' that this setback to his peace initiative is only a temporary one. But unless he is prepared to take decisive steps to persuade leaders of the Palestine Liberation Organization to approve the Jordanian monarch's participation, his initiative is in jeopardy. It will take strong leadership to keep the plan alive.
Who is to blame for the breakdown?
The Arabs certainly have not helped. King Hussein had wrapped up an agreement with PLO leader Yasser Arafat for joining the talks, but the agreement broke down after Arafat touched base with other Palestinian leaders. Once again the Arabs seem to be losing an opportunity to negotiate with Israel. They have done so often in the past - always at their own expense. When will they be willing to take a risk for peace?
However, in fairness it can be said that PLO leaders are afraid of walking into a trap - sitting down to talk with Israel while the latter continues its occupation of Lebanon and, not least of all, its colonization of the West Bank. What the PLO wants, and understandably so, is a commitment from the US that it can and will persuade Israel to negotiate - and to negotiate in good faith.
At the moment the Arabs have no such commitment. Israel has rejected the Reagan plan outright. Nor is there any sign that Washington has influence over the Begin government. The record speaks for itself: The US was unable to forestall the Israeli invasion of Lebanon. The US was unable to stop Israel from bombing west Beirut even after Israeli forces had already won the war against the PLO. The US was unable to protect the Palestinians in the Israeli-controlled Shatila and Sabra camps from slaughter by Phalange forces, though the US had promised the PLO that the refugees would be safeguarded.
Now the President says he will ''try'' to persuade the Israeli government to freeze settlement activity on the West Bank while negotiations get under way. Unfortunately, ''try'' is not a convincing word. Why, the Arabs can reasonably ask, should the Palestinian leaders believe that Mr. Reagan will succeed where others have failed? The US has urged Israel for years now to stop building Jewish settlements in the West Bank, all to no avail. In defiance of Washington's importunings - not to mention international law - Israel has simply accelerated its gradual absorption of the West Bank territory taken by force in war.
The question is no longer what Hussein will do but what the United States will do. If President Reagan hopes to rescue his peace effort, he must be prepared for stronger action and, perhaps, a modified approach. These elements are crucial:
* A Lebanese-Israeli agreement on the withdrawal of Israeli forces from Lebanon. Inasmuch as Israel has violated American law regarding the defensive use of US-supplied arms, there is no reason why the US should continue to provide weapons for the occupation of Lebanon. More than delaying the long-term sale of F-16s, Mr. Reagan should consider cutting back aid actually in the pipeline.
* An Israeli freeze on further settlement of the West Bank and Gaza. It should not escape world notice that the Israeli government, in addition to speeding colonization of the area by Israelis, is now promoting the sale of West Bank land to American citizens. According to columnists Evans and Novak, some 300 Jewish citizens gathered in New York City in March to hear Israeli officials solicit sales - $3,800 for a fourth of an acre, to be exact. Israel has no legal or moral right to sell to foreign nationals land which it seized in war and which it controls as an occupying power. The US has no legal or moral right to support such a policy.
* An American commitment to ''self-determination'' for the Palestinian people. It is not entirely clear why PLO leaders turned down the Hussein-Arafat agreement, but they have long been skeptical about endorsing the Reagan plan which makes no mention of ''self-determination.'' Surely President Reagan can find some way to use this term publicly, thereby reassuring Palestinian leaders and removing a political and mental block to negotiation.
The Arabs should rethink their position, bearing in mind the negative image they convey in the world when they seem to be resisting negotiation. Their posture does not make things any easier for the United States.
The President, for his part, also has some rethinking to do. Does he have the political will to pursue his initiative? It is not a matter of the US pressuring Israel. It is a matter of the US upholding the principles of international law. It is a matter of the US abiding by American laws and pursuing its own national interest. It is a matter of the US helping Israel to see that only through peace with its neighbors can its long-term survival be assured - a vision shared by many Jewish Americans and Israelis.
As he weighs his next move, the President should know that more is at stake than the Arab-Israeli dispute over the West Bank. The Israeli invasion of Lebanon has brought in its train a whole array of new problems. The chaos in Lebanon, the Iran-Iraq war, the rise of Muslim fundamentalism, the growing presence of the Soviet Union in the Middle East - these are the elements of a potentially explosive brew.
Mr. Reagan has the power to prevent that explosion.