IT IS SAD that Jordan still can't see its way to sitting down with Israel. Who knows when, or if, as good an opportunity for peace may arise again? Still, you can hardly blame King Hussein, given his absolute requirement not to get out of step with the PLO. He tried, and for awhile it looked as though Yasser Arafat would join a negotiating partnership with him. But Mr. Arafat suddenly changed his mind, or couldn't swing key factions, or was intimidated by hints of the violence that killed his moderate colleague in Portugal, or was pressured or bought off by Syria or Libya, or whatever.

Consultations continue, the Reagan administration insists. But there should be a difference. In the four years since Camp David created the Palestinians' first new political opening in 30-odd years, and in the seven months since President Reagan reshaped it, the PLO's frailties have become apparent. No one concerned with Palestinian dispersion and disenfranchisement can count on the PLO. It lost its last military option in Lebanon last summer and it may now have cast away its lone live political option. By insisting on getting all--a precooked Palestinian state--it ensures it gets nothing.

It will be said that the PLO's default leaves Israel morally as well as politically free to consummate the annexation of the West Bank. But the Palestinian people cannot be penalized indefinitely for the shortcomings of the PLO. Notwithstanding the huge boost the Arafat negativism gives to Israeli annexationists, it is wrong for the future of the occupied territories to be decided by force alone.

The key fact is that the statehood-or-nothing approach of the PLO has only feeble support among West Bankers. Their priority is to stop the pouring of Israeli concrete--"to save the land," as King Hussein put it: to end or ease the Israeli occupation. Those who would be constructive now must find ways to encourage this pragmatic gradualist temper.

President Reagan will now be faulted for the moderation of his Sept. 1 plan and for not playing his hand with enough skill or muscle. But his plan was right, designed as it was to provide Israel a negotiating partner and the Palestinians a homeland. And no American diplomatic method can satisfy absolutism of the PLO's sort.

It would be foolish to chase further after the PLO. But it would be shortsighted not to continue the effort to draw out a Palestinian negotiating partner on the West Bank. No one can be sanguine, but it remains so that only in negotiations can Israelis be expected to make the concessions and, they should understand, reap the benefits that add up to peace.