Like Ronald Reagan in the first presidential debate, I don't want to say it, but I can't help myself: There they go again.

Once again, the nation's political leadership -- Republican, Democratic -- is shocked, chagrined and outraged. The cause this time is a CIA-produced manual called "Operaciones Sicologicas en Guerra de Guerrillas" that was apparently distributed to the so-called contras who are fighting Nicaragua's Sandinista regime. It tells how to fight dirty.

It tells how and when to kill innocent civilians, how to implicate and involve the local population in such acts, how to stir up mob action and how and under what circumstances thugs and criminals can be used. The CIA says it was written by a low-level free-lancer and does not reflect American policy. If you believe that, possibly I can interest you in a share of the Brooklyn Bridge.

Once before, you will recall, there was similar shock, chagrin and outrage. That was when it was discovered that the CIA was responsible for mining Nicaraguan harbors. Several ships, including a Soviet one, were slightly damaged and Nicaragua accused the United States of mining its ports. The U.S. stayed mum -- until the news media reported that the mines in fact had been laid with American help. Then the same members of Congress who support the covert war against Nicaragua bleated their outrage. Just who they thought had been laying the mines they did not say. Possibly it was the Mickey Mouse Club.

Now we once again have an explosion of false outrage. We are told it's against the law for the CIA to instruct others in the killing of innocent civilians. It is un-American to use "selective violence" to "neutralize" members of the Sandinista regime -- to choose them ahead of time on the basis of "spontaneous hostility that the majority of the population feels against the target." Even aside from that, we are told that this is not the way we Americans fight.

But what, dear readers, did all these politicians think was happening before the manual was leaked to the Associated Press? How do they think you fight a covert-overt dirty little war waged by mercenaries, some of whom would not fight if the checks stopped coming? After all, some of the so- called "freedom fighters" President Reagan extols are former members of Anastasio Somoza's National Guard, an outfit of thugs and sadists best known for rape and torture. They need a manual on killing the way a goldfish needs swimming lessons.

The CIA-produced manual represents the second time the United States has lost its virginity in Nicaragua. It goes without saying that this cannot persist without a certain loss of credibility. Congress cannot continue to be shocked to find that after it has authorized and funded a war, it is actually being fought. The Sandinistas are the best witnesses to what's happening. They said their ports were being mined, and they were. They say that civilians are being killed, and, it seems, they are.

The shock and the outrage should instead be reserved for the war itself. Instead of questioning the methods, Congress should wonder if the war is either necessary or right and whether we lose more than we gain. For instance, a quick reading of even excerpts from the manual would confuse anyone about its source. It could have been written by agents of a totalitarian government, maybe communist. It is a cynical and amoral document that in no way represents either the ethics or the morality of most Americans or what this country stands for.

The CIA manual is neither a scandal nor a mistake, but an admission. It suggests that only lies and terror can pry the Nicaraguans away from their government. If it's necessary to lie to the local population, to select government officials and kill them, to employ criminals and thugs, to indoctrinate the people, to encourage vigilante justice by using "false statements from citizens," to advocate the killing of innocents so as "to create a martyr for the cause," then, like Vietnam, we are once again fighting the wrong war for the wrong reasons.

The true outrage is not the manual itself, but what it concedes. In Nicaragua, we have become indistinguishable from the portrait we paint of our enemy. Win, lose or draw, it's all the same. We can only lose.