An intriguing hint of potential PLO flexibility has come to light, courtesy, ironically, of Israel, whose embassy in Washington has assembled a fat stack of assorted documents captured by the Israelis in their sweep through Lebanon. They are powerful reinforcement for much of what the Israelis and others have been saying all along about the PLO: its worldwide terrorist links; its tight connection (training, arms, political support) with the Soviets and the Communist bloc.

But they also include an astonishingly revealing glimpse of the Soviet/PLO relationship at work. You find it in a document described as the "protocol" (written record) of a meeting at the Kremlin on Nov. 13, 1979, between Soviet Foreign Minister Andrei Gromyko and a PLO delegation led by a certain Abu Amer--a code name for Yasser Arafat.

Now I don't know what a copy of this document was doing in a PLO camp somewhere outside of the PLO's Beirut headquarters. But if we are expected by the Israelis to accept the authenticity of the rest of this captured material, it seems reasonable to give some weight to this one--and to the likelihood that Gromyko and Arafat, behind closed doors, were not exchanging propaganda.

So I would put it down as of some significance that we find Gromyko, three years ago, very nearly plaintive in his pleading with Arafat to give some thought to accepting Henry Kissinger's terms--and Arafat responding with complaints that he had been sending out feelers and getting no response.

"Are you considering certain tactical concessions in return for getting recognition from the hostile camp?" Gromyko asks. And then, specifically: was Arafat "considering recognizing these (U.N.) resolutions? Are you also considering recognizing Israel's right to exist as an independent sovereign state?"

Gromyko was polite ("Please regard it as a question only") but firm: "the Americans" were bugging him; it's "demagoguery, but we have to know how to deal with it. . . . In our talks with the Americans we always confront this obstacle which cannot be overcome. . . . I ask you to think about it."

Now it was Arafat's turn to be plaintive. He was ready to answer Gromyko's question "if it will lead to any results, since it indeed deserves an effort on our part." But, said Arafat, the PLO had tossed out hints regularly. "Knowing that we are the victim," he said, "we raised many possible solutions, while none of our enemies presented any."

He spoke of a 1974 offer by the PLO to "establish the Palestinian state on every part of land which Israel withdraws from or which will be liberated." This, he seemed to be saying, was not the same thing as calling for Israel's liquidation. And he made cryptic references to what appear to be contacts with the Carter administration in 1977, in which a U.S. offer was made to exchange PLO support of an amended resolution 242 for the opening of a dialogue and U.S. recognition of the PLO--a proposal that he said the United States later withdrew as the Camp David process got under way.

If the PLO and the Soviets were secretly talking this way in 1979 about "concessions," when Arafat had a sizable army, Israel had not yet made peace with Egypt, and the Israeli hold on the West Bank was far less advanced, it would be interesting to know what the private attitudes of both parties are today.