LAST SUMMER in Lebanon, the Palestine Liberation Organization suffered a military rout, a forced removal and dispersion of almost all its fighters and, as a result, the loss of any military option other than isolated acts of harassment and terror. The Palestinian national movement, or the part of it represented by the PLO, has been trying since to recover from the shock. The current meeting of its "congress," the Palestine National Council, in remote Algeria was widely seen to be its moment of political truth. Could the PLO start to deal constructively with the aftermath of the long hot summer in Beirut --its defeat, the new American peace plan and Israel's relentless colonizing on the West Bank?

From Algiers, the answer is now just about in. A leading PLO moderate, Issam Sartawi, had called publicly for recognition of Israel by way of winning a dialogue with Washington and thereby getting into the circle of diplomacy where all action is now confined; denied the floor by chairman Yasser Arafat, he resigned. A leading extremist, George Habash, won thunderous applause by denouncing "this shameful and disgraceful Reagan plan" that "says no to a Palestinian state and no to the PLO," ignoring that the plan would end the Israeli occupation and establish an Arab sovereignty in the West Bank. Mr. Arafat himself, as usual, was enough different things to enough different people to maintain the unity of the PLO--and its virtual paralysis.

The Algiers meeting has seemed so consistent with Israel's own rejection of the Reagan plan that a cynic might call it "Begin's congress." For the PLO largely put organizational convenience over political revival. It assured itself a continuing position on the far fringe, with little influence, of international diplomacy. It widened the gap between itself and the people of the West Bank, who, being fully aware of the march of the Begin annexation policy, cannot indulge the fantasies that still distract Palestinian politicians in exile. The curse of the Palestinian movement remains its tendency to leave the destiny of its people in the hands of others.

So the PLO has failed its test. How will King Hussein meet his? Very soon he may say whether he accepts President Reagan's invitation to talks on the American plan. The king has made a career of saying no, and he and his friends and his disparagers have prepared the stuff of a dozen alibis. Many of those alibis center on the failings, real and imagined, of American policy. Why should King Hussein join the talks? For the familiar reason, never out of date: to take a risk for peace.