What do Mikhail Gorbachev, Saddam Hussein and Yitzhak Shamir have in common? Not much, each would answer with speed and reason. But there is a thread in recent events that connects them. Their actions and words should focus our thinking about the relationship between political leadership and political violence.

By an accident of timing, Gorbachev prepared to sit down with President Bush at the Washington summit to talk peace just as Arab leaders were sitting down at the Baghdad summit to endorse economic, political and, if necessary, military war with Israel. The television screens and newspaper pages that juxtaposed these events were unconsciously illustrating two differing reactions to the use of political violence as the 1990s begin.

Gorbachev first. He has proved that his much abused mentor, V. I. Lenin, got at least one thing right: communism can be implemented only in a system based on political violence. Withdraw the threat of violence, and the populace will quickly evade or overturn communist rule.

That is the irreducible lesson of what has happened in Eastern Europe and what is now happening in the Soviet Union. By abandoning the indiscriminate use of political violence, Gorbachev condemns Marxist-Leninist rule in its ideological homeland. Looking on from the Big Kremlin in the sky, Lenin and Leonid Brezhnev must take grim satisfaction from Gorbachev's convincing demonstration that communism with a human face collapses as soon as people are given a true choice.

We must knock on wood and acknowledge that organized violence is still used as a tool of political control in the Soviet Union. (See: Lithuania, Azerbaijan.) But it does seem to me that Gorbachev has made the Soviet Union part of a larger trend in industrial countries away from killing, imprisoning or abducting to impose political values on unwilling subjects or societies at large.

The Red Brigades of Italy, the Baader-Meinhofs of West Germany, the East German Honecker-type regimes fade like bad dreams for European political movements that until recently subscribed to the omelet theory of history: you had to break eggs to make the omelet of a more just tomorrow. People had to be coerced, intimidated or even killed for their own good.

The first anniversary of the Tiananmen massacre reminds that China's Communists are among those who still subscribe to this rationalization. And that spirit hovered over the Arab League summit in Baghdad, which was a meeting founded on political violence.

Many Arab leaders came out of fear that the Iraqis would punish them if they stayed away. Even if you are the king of Saudi Arabia or the president of Egypt, you respond to the common denominator of Arab politics: fear of retaliation by someone who is more powerful, richer or more evil than you are; someone who is ready to break eggs.

Moderate Arab leaders who fell into line with Saddam Hussein's denunciations of the United States and Israel have allowed the Iraqi president to establish himself as the leader who sets the tone and pace in the Arab world today. They have ratcheted up tensions in an already explosive climate.

In the Middle East, one man's political violence is still another's terrorism. The dominant voices on each side cling to the kind of rationalizations about political violence that Gorbachev and others have shown can -- and should -- be abandoned.

American officials knowingly stepped into this pool of quicksand 18 months ago by starting a dialogue with the Palestine Liberation Organization conditioned on the PLO not committing acts of terrorism. The condition posed two questions that may be beyond the capacity of even diplomats to answer or fudge: What is terrorism? What is the PLO?

The arrival on an Israeli beach of a speedboat carrying gunmen from one PLO faction intent on murder should bring the argument between Washington and Jerusalem over defining terrorism and the PLO to a head. Even if the dialogue is broken off, it will have had two useful consequences, one intended, the other not.

The carrot of dialogue and possible recognition by the United States has clearly restrained the PLO from terror actions during the past 18 months. And the dialogue has exposed the difficulties, and even contradictions, of trying to make exact distinctions among different types of political violence and the causes they serve.

Israel's armed forces engage in violence for the political and strategic cause of keeping the West Bank under Israeli control. Shamir's policies would extend that control -- and that violence if necessary -- into the future indefinitely. To the Palestinians of the intifada, this is terrorism. To Shamir, it is the intifada that is terrorism. He is taking only necessary countermeasures.

The point is not to suggest that there is a moral equivalence between Israeli and Palestinian actions and motives. The point is that even ''necessary'' violence can -- usually does -- corrupt and undermine the political cause it initially serves. Gorbachev appears to have understood this and acted on his understanding. Only by doing the same can the leaders of the Middle East end the region's cycle of disaster.