Old joke. First man: Do you cheat on your wife? Second man: Who should I cheat on, my uncle?

Before someone yells "Get the hook," examine the logic of the joke and then see if it does not apply to Israel's refusal to negotiate with the Palestine Liberation Organization. Israel bases its refusal on the PLO's being a terrorist organization that has never recognized Israel's right to exist. That's true. But as the joke suggests, who can you make peace with if not your enemies?

To that question, Israel has a stock answer: Palestinian moderates. These, though, are the tooth fairies of the Middle East. The Israelis have managed to eliminate whatever moderate Palestinian leadership existed on the West Bank or in the Gaza Strip. Palestinian leaders who were openly hostile to the continuing Israeli occupation were either removed from office or, in some cases, banished to Lebanon. The result is that Palestinian moderation has become an oxymoron. Uncle Toms may be moderates, but they are not leaders.

As usual, when it comes to making a bad situation worse, the Israelis have had help from the Arabs -- in this case the PLO itself. When from time to time a Palestinian leader does assert himself and say the time has come to sit down and talk with the Israelis, he has a tendency to be killed. This is precisely what happened in 1979 to Sheik Hashan Hussendair, the Gaza Strip's ranking Moslem leader. The lesson of his murder, claimed by the Palestine Liberation Front and applauded by the PLO itself, has not been lost on other Palestinians who think they can go their own way. The PLO simply will not allow it.

This is reality -- the reality of Israeli policy, the reality of PLO violence. Domestic Israeli politics also is a reality, and it responds, as any nation's would, to the killing of civilians by PLO terrorists. The cold-blooded killing of children indelibly stains the PLO. Pity the Israeli politician who suggests talking to the killers of babies.

So maybe it would be instructive if Israel looked to South Africa for some perspective. There, the government refuses to negotiate with the outlawed African National Congress for the same reasons Israel will not talk with the PLO: the ANC is responsible for terrorism and will not renounce violence. Nevertheless, it is so apparent to neutral observers that unless Pretoria talks with the ANC leadership things will only get worse, that even the United States, which supports Israel's policy of not talking with the PLO, has urged South Africa to reverse its policy.

What is true for Pretoria and the ANC is true for Israel and the PLO. In both, a government will not negotiate with its enemy because it is, manifestly, its enemy. Especially in Israel's case, where the cost of terrorism has been high, the sentiment is understandable. But the counter sentiment is Palestinian nationalism, and as long as the PLO carries that flag, it will have to be seated at any bargaining table. Ironically, it is precisely through terrorism -- the willingness both to die and kill for its cause -- that the PLO asserts is credentials as the sole representative of the Palestinian people. When the United States and others ask the PLO to renounce violence and recognize Israel, it in effect asks the PLO to cease being the PLO. It's an offer the PLO finds difficult to accept.

The upshot is an impasse. There can be no peace in the Middle East without the acquiescence and participation of the Palestinians. No one, not even the king of Jordan, can negotiate for them. And whether Israel and the United States like it or not, the PLO speaks for the Palestinians -- even if its leadership was seized at gunpoint.

Sometimes peace is harder than war. Sometimes you have to sit down opposite the killers of children, the murderers of women or, from the Palestinian perspective, the bombers of Beirut, and talk with your enemy. But there is truth to the old joke. If you can't make peace with your enemy, who can you make peace with? The answer in the Middle East is distressingly obvious.

No one.