The seizure of the Iranian Embassy in London the other day bore a relation to the seizure of the American diplomats in Tehran. It was also connected with the intermittent, subsurface warfare waging between Iraq and Iran.

Those links announce the first lesson of the London siege. It is that terrorism moves in waves. One incident makes room for another. The disease is catching, and despite the deterrent effects of the police action in Britain, there is almost certainly more trouble in the wings.

The second lesson is that no one can be sure where the fever will break out next. Terrorist actions are carried out by tiny groups -- five to 50 people. The terrorists dwell in a strange, half-lit realm far less well known to the police than the underworld. They are dedicated to the point of fanaticism, and rarely turn informer. So it is unusual that terrorists are apprehended before they strike.

Efforts to establish a geography of terrorist actions quickly break down -- sometimes ludicrously. Walter laqueur, on whose work I draw heavily in this column, once noted that it could be argued that "there is a connection between terrorism and soccer, for the four countries which finished on top in the world championships of 1978 were all affected by terrorism (Argentina, Brazil, Holland, Italy)."

But if there is no logical pattern to the strikes, there is a well-known infrastructure. Terrorists don't come from just anywhere. They are highly trained. They are well equipped with weapons. They bear passports and other forms of identity not readily available. They depend upon established groups for support. They work out of countries that make no secret of their enthusiasm for terrorist activities.

Submerged nations denied statehood are typically prone to use the terrorist weapon. The Zionists did it before the independence of Israel.

Now the Palestine Liberation Organization is central to the international terrorist network. The PLO accepts terrorism as a legitimate form of pressure, and has repeatedly claimed credit for various strikes. Many terrorists are themselves Palestinians. Terrorists from other lands -- Germans, Italians and Japanese, for example -- are known to have worked with the PLO.

In a different category are the self-styled revolutionary governments that patronize terrorist operations. Cuba, of course, is the celebrated example in this hemisphere. Libya and South Yemen fit the bill in the Middle East. Iraq, which has a notorious reputation in this regard, seems to have been involved in the London shootout. It is noteworthy that its leader, Saddam Hussein, made his debut in big-time politics back in 1959 as a participant in the abortive effort to assassinate Iraq's then-president, Abdul Karim Kassem.

Russia, it is also worth noting, supports the terrorist operations in the Middle East and elsewhere. Whatever may be said of dirty work done by the Central Intelligence Agency, no account is complete without a rendering of similar work done in the past, and still organized, by the Soviet Union.

A final lesson of the Longon drama is that successful resistance to terrorism depends importantly upon the determination and nerve of the affected government -- and the social cohesion of its people. Mrs. Thatcher's government in Britain showed itself to be unflinchingly resolute in dealing with the terrorists. No one can doubt Mrs. Thatcher had the united backing of the British people.

Other governments, with less steady public support, have wavered -- with unhappy results. Italy, until recently, presented the classic case in point. West Germany and Japan have also waffled. It has been observed that all three were losers in World War II. It appears that bitter memories of the police-state regimes that brought the countries into the war yielded an aversion to the use of any force by the state.

The United States, perhaps as a result of Watergate and Vietnam, tends to range itself with the losers of the last big war. In hostage situations, the inclination has been to show patience and restraint, and even to look around for mitigating circumstances -- reasons to feel guilty.

Some signs suggest a stiffening of public attitude in this respect. I am not so sure. But if so, it is all to the good. For a critical element in the fight against terrorism -- and indeed, in the reordering of world politics -- would be a disposition by the United States to formulate a distinct policy of making life tough for Cuba, Libya, South Yemen and other pipsqueak countries that center their foreign policies on the fomenting of terror.