THERE IS entirely too much talk lately about nuclear war. First we had Secretary of State Alexander Haig testify in front of a Senate committe that there were worse things in this world than nuclear war. Then we had Secretary of Defense Caspar Weinberger pushing for a neutron bomb. Everyone suddenly seems to be thinking the unthinkable.

My friend Alabaster, who is getting nervous about all this nuclear saber-rattling, has a theory as to what is causing it.

"The problem is that for 35 years our measuring stick for atomic holocaust has been Hiroshima and Nagasaki.

"Every time someone wants to make an atomic weapon comparison he says: 'This warhead packs 1,000 times the wallop of the bomb dropped on Hiroshima.' Or 'This artillery shell will give you 30 times more punch than what we did to Nagasaki.'

"These stats don't have relevance anymore. Hiroshima and Nagasaki are part of ancient history and have no meaning for the people running the world today. We have to come up with a new yardstick to give them some idea of what atomic weapons can do."

"I have a modest proposal," Alabaster said. "We need two new examples to demonstrate how awesome nuclear war is, so it will sober up politicians, military men and statesmen, not only here but in the Soviet Union."

"All right," I agreed. "What do you have in mind?"

"We should permit the United States and the U.S.S.R. to fire off their largest nuclear weapon at just one Soviet and one U.S. city, to prove how powerful the weapons really are."

"Why not?" I asked.

"Moscow and Washington would be off limits because we don't want to eliminate the leaders of both countries, or the lesson would be lost on them," he continued. "We must select two beautiful cities that have tremendous sentimental meaning for the people of the respective countries. I would suggest the U.S. 'nuke' Leningrad, and the U.S.S.R. 'nuke' San Francisco."

"Why Leningrad?" I asked.

"It is without a doubt the loveliest city in the Soviet Union, the magnificent palaces, irreplaceable architecture, and one of the great museums of the world."

"Why San Francisco?"

"Everyone loves San Francisco. One easily can leave his heart there."

"What will it prove?" I asked.

"When the Russians see the devastation one American weapon has done to its beloved Leningrad they will realize that the United States is not stockpiling Tinker Toys.

"And in turn the Americans who have been discussing nuclear war as some kind of military Super Bowl will have second thoughts about solving its foreign problems with atomic weapons. With Leningrad and San Francisco 'nuked,' we won't need Hiroshima and Agasaki anymore to point out the dangers of a new war.

"But my modest proposal has a second benefit. We and the Soviets have spent a bundle on nuclear arms, and both sides deserve to shoot off at least one in anger during our lifetime, if for no other reason than to see firsthand that we got our money's worth."