A FUNDAMENTAL reason why our intelligence agencies, military leaders and (above all) Washington pols can’t understand Afghanistan is that they don’t recognize that we’re dealing with alien life-forms.

Oh, the strange-minded aliens in question resemble us physically. We share a few common needs: We and the aliens are oxygen breathers who require food and water at frequent intervals. Our body casings feel heat or cold. We’re divided into two sexes (more or less). And we’re mortal.

But that’s about where the similarities end, analytically speaking.

In my years as an intelligence officer, I saw colleagues make the same blunder over and over: They rushed to stress the ways in which the Russians, the Chinese or the Iranians were “just like us.” It’s the differences that kill you, though.

I was an effective intelligence officer. Why? In junior high, I matured past the French Existentialists and started reading science fiction. The prose was often ragged, but the speculative frameworks offered a useful approach to analysis.

Begin with the view that all opponents are aliens from another cultural planet. Build your assessment from a blank slate. What do the alien collectives desire or fear? How do they perceive the galaxy? What are their unique weaknesses?

Regarding Planet Afghanistan, we still hear the deadly cliché that “all human beings want the same basic things, such as better lives and greater opportunities for their children.” How does that apply to Afghan aliens who prefer their crude way of life and its merciless cults?

When girls and women are denied education or even health care and are executed by their own kin for minor infractions against the cult, how does that square with our insistence that all men want greater opportunities for the kids?

What about those Afghan parents who approve of or even encourage suicidal attacks by their sons? This not only confounds our value system, but defies biological reason.

So: These humanoid forms with which we must deal don’t all want or value the same things we do. They form different social aggregates and exchange goods and services within wildly different parameters (and exhibit hypocritical sexual tastes that diverge from procreative mandates – ask our troops about that).

These alien tribes seek to destroy physical objects and systems valued on Planet America. They perceive time differently. They treat other life forms more harshly than we do. Their own lives are shorter, with different arcs. They quite like our weapons, though . . .

The point isn’t to argue that Afghans are inferior beings. It’s just that they’re irreconcilably different beings – more divergent from our behavioral norms than the weirdest crew member of the starship Enterprise.

As an analytical exercise, try to understand Afghanistan as a hostile planet to which we have been forced, in self-defense, to deploy military colonies. How do the bizarre creatures on that other planet view us? What do they want? What will they accept? Is killing us business, pleasure – or both?

Are there tribes among these aliens with which we can cooperate? Which actions of ours inflame the alien psyche? What will the alien willingly die for? What does the alien find inexplicable about us? Must we preserve a useful climate of fear?

Do we intend to maintain our military colonies out there in deep space? For how long? Can the angry planet ever be sanitized of threats?

Of course, there’s more in play than images of our “starship troopers” combating those alien life-forms that call themselves “Taliban.” This exercise is just meant to break our mental gridlock, to challenge our crippling assumption that we’re all merry brothers and sisters who just have to work through a few small understandings.

This is a “war of the worlds” in the cultural sense, a head-on collision between civilizations from different galaxies.

And the aliens don’t come in peace.

Ralph Peters’ latest book is “Looking for Trouble: Adventures in a Broken World.”