Suppose I tell you a story about a puppy. Its owner slapped it, kicked it and otherwise abused it, and then one day it bit someone who reached to pet it. The owner said he just couldn't understand why the puppy had bitten someone but as the owner, his options, as they say, were limited. He put it to sleep.

Whether there is such a puppy and such an owner somewhere I do not know. But I do know that if you think of the United States as the owner and Nicaragua as the puppy you will have a pretty fair analogy of what's going on in Central America. Having slapped around Nicaragua since almost 1979 when Anastasio Somoza fled into exile, the United States is now shocked and outraged that Nicaragua is fighting back. The Sandinistas government has called its friends, the Cubans, for help.

It is necessary when writing about Nicaragua to follow certain rules, and I will do so. First you must condemn the Sandinista regime, point out that it is anti-democratic, abuses civil liberties, censors the press, is avowedly Marxist, has close ties to both Moscow and Havana, is increasingly corrupt and has betrayed its own revolution. And then you have to say that the United States could never tolerate Soviet MiGs or missiles of any kind in Nicaragua.

The other rule to follow is to point out that the counterrevolutionaries, the so-called contras, are no longer just the creation of the CIA. From an original nucleus of mercenaries, the movement has expanded to include some dissident politicians, dissatisfied peasants and young men fleeing the government's draft. It seems that if they have to fight, they would prefer to fight their own government. That kind of thing gets you a lousy bond rating.

It is understandable, therefore, that you may find it hard to root for either side. Fine. But that should hardly stop you from asking where things are going. In the beginning, there was only the Sandinista regime, and then the CIA created the contras. Now the Sandinistas are fighting with helicopter gunships they didn't used to have and the contras have responded with Soviet SA-7 surface-to-air missiles. The Sandinistas certainly have Cuban advisers, probably helicopter pilots, maybe even combat troops. Shall we up the bidding some more? Certainly, says Secretary of State George Shultz. After all, there are Cubans in Nicaragua!

Here you have the dog finally biting back. To the Reagan administration, Cuba is one of those electroshock words that tingles the mind, blocks all thinking and produces blurred visions of San Juan Hill. But it was predictable that Nicaragua, in extremis and duress, would turn to an ally for whatever help that ally would provide. after all, fighting for its life and -- it is worth pointing out -- on its own soil. How would any nation react if one of its helicopters were downed within its own country?

Time and time again, the Reagan administration avers that it is not out to topple the Sandinista regime. Yeah, and the check is in the mail. It also says that it will never send U.S. troops to Nicaragua. By every indication, that is a more serious pledge but one that could wind up the captive of events. The administration seems determined to escalate the conflict and, at the same time, keep it within certain bounds. But a thermostat to keep wars within limits has yet to be found.

What will happen if the Soviet Union, up to now distracted by Afghanistan, decides to take an interest in Nicaragua? The Soviets surely know better than to ape the Cubans, but they can still provide lots of aid. What will happen if Nicaragua, with Soviet assistance, makes good on its veiled threat to turn up the level of fighting in nearby El Salvador by supplying the guerrillas there with surface-to-air missiles?

The fact is that within certain limits almost anything can happen. By applying pressure, the United States is turning the Sandinista regime into a totalitarian regime that's in an almost total frenzy. It makes miscalculation after miscalculation, insults its friends in Congress and elsewhere in the world and, fighting for its very existence, snaps at anything that comes near it. Like the mistreated puppy, it may have to be put to sleep. Who, they'll ask, could have predicted it?