IT WAS A sweet party that Jordan's King Hussein hosted in Amman. A couple of Palestinian terrorist leaders were there for the first time since their attempt to topple the king in 1970 led him to drive them out and kill thousands of their comrades. (Israel then saved him when Syria sent in tanks.) A Libyan was there to extol the glories of suicide car bombs. The conference, bringing together Saddam Hussein's Arab supporters, appealed for the overthrow of Egyptian President Hosni Mubarak and declared an intent ''to strike against American interests everywhere and by all means" if the United States attacks Iraq.

The urbane "moderate" King Hussein rarely loses an opportunity to lecture the West on the values of cooperation and peace. In the Gulf crisis, however, he has tilted heavily to the side of the aggressor, Iraq, alienating his old friends and patrons. One purpose has been to conciliate his Palestinian majority, large parts of which greeted Saddam Hussein's capture of Kuwait as prelude to the liberation of the West Bank. This helps explain why King Hussein gave a stage, sounding board and personal audience to the conferring Arab radicals, people who can only have contempt for a leader like him whose sources of power are largely foreign and whose principal goal is to preserve his throne. It was a pathetic performance.

It is tempting to write off this exasperating figure, to say he has come to the end of his 37-year road of maneuver, public relations and evasion. Few political leaders have been more wrong more often. He failed to give West Bank Palestinians political rights when he could have before 1967. In the 1967 war, he rejected Israel's offer of a free pass, invaded and lost the West Bank. In 1988 he prematurely released his lingering grasp on the West Bank for nothing. Now he has made an immense gamble on Saddam Hussein.

Even so, he has an undeniable convenience value. If he did not exist, he would have to be invented: as a buffer between Israel and Iraq -- a buffer more vital for the weakening of Iran as a strategic check on Baghdad -- and as, still, a potential natural partner for an eventual peace engaging Israel and the Palestinians. Any likely successor in Amman would be a Palestinian who in the circumstances could not be expected to exercise even the king's unreliable measure of restraint.