JORDAN'S KING HUSSEIN completed a quiet tour de force on his Washington visit. He is, after all, the fellow whom the United States has cultivated for decades, whom the administration counted on to make Camp David work on the West Bank and who has refused to go along. If American diplomacy in the Middle East is stuck, he is one of the principal reasons why. In Washington, nonetheless, he was treated like . . . well, like a king: received at the highest levels, consulted, dined, praised and, to top it off, offered a big new batch of American tanks. Administration officials went out of their way to conceal their regret and to convey their understanding of his rejection of their diplomatic program. The king could be pardoned for wondering whether it would have brought him any more to be actually cooperating with, rather than confounding, the United States.

Why is this so, and why is this, as it is, a necessary though hardly desirable state of affairs? The simple reason is that as long as the basic thrust of American policy on the West Bank is to ensure a moderate outcome there, the United States has no alternative to working closely with Jordan. If this is not possible now while Menachem Begin is in power in Jerusalem, then perhaps it would be possible later with another Israeli government. King Hussein, a survivor, will probably still be there. In fact, it is not only a tenet of American policy to keep Jordon on hold, as difficult as that may be while King Hussein calmly says no to Camp David. It is a tenet of Israeli policy, or more precisely of the policy of the "Jordanian option" -- dealing off West Bank Palestinians to King Hussein in return for security considerations -- that a Labor government would be expected to explore. It's that simple.

That leaves Jordan sitting pretty -- if living well on the side of a volcano that has erupted before and could erupt again fits that term. By keeping political faith with the PLO and detaching himself from Camp David, King Hussein has earned himself as solid a place as he has perhaps ever enjoyed in the "Arab family," not to speak of a billion or two dollars in annual subsidies. At the same time, by keeping Jordan out of the PLO's guerrilla war, by doing what he can to cushion the impact of military occupation on the West Bank and by holding himself available for later diplomatic duty, he retains the reputation for moderation that has long been his passport to good standing in the West. He is a vexing fellow, but he is valuable, too. American disagreements with him, though severe in appearance, are softened in reality by a common hope for peace.