The Israleis in releasing 31 Lebanese prisoners (26 Shiites, six Sunnis), did something genuinely difficult and courageous. In the face of deep public anxiety and keen political peril, the government of Shimon Peres went ahead without the cover of a public American request and took a good- faith step to break the hostage stalemate.

Mr. Peres insists that the release was made according to a plan on which Israel previously had settled for reasons of its own. No responsible person will quibble with him. Nor will any responsible person deny him credit for acting in a way that is bound to be interpreted, in many quarters, as 1)caving in to terrorists and 2)setting a precedent for Israel's pulling American chestnuts out of a fire.

So what is Nabih Berri doing? Wy is he not exhibiting some of the same courage and statesmanship on view in Israel? One hears much learned talk about the political predicament he is in, about the limits on his freedom of action and maneuver, and so on. Frankly, it interests us a great deal less than does the predicament of the American hostages: one is dead and 40, plus the seven Americans seized in Beirut earlier, remain cruelly exposed to their captors' whims.

Mr. Berri, who voluntarily assumed responsibility for the TWA group, has taken to threatening those who ask him to fulfill his responsibility. He suggests he will abandon it and turn the hostages back to Shiite hands ostensibly less careful than his own if the crisis is not played out his way. But protestations of limited and divided authority will not do. Yes, Mr. Berri is in a tough spot. His friends will help him to get out of it by taking a tough decision: to keep alive the process the Israelis have begun. The next move is his.

In Washington, there is a heavy emphass now on the sending of signals, one set meant to convey a capacity for action and another a capacity for restraint. These signals are meant to be received for the most part by unfriendly and suspicious parties not open to the normal considerations affecting the relations of states. But there is more to policy than the sending of signals to parties that may or may not receive the ones we intend.

At the heart of policy necessarily lies the relationships the United States maintains with those who are sympathetic to American interests. The Israelis, with all too much experience of their own in the matter, understand the high value Americans place on the safety and mobility of their citizens. This is precisely what Nabih Berri, and any others who might be drawn into a helpful role, must understand as well.