Early in this century, a retired British colonel wrote a book about "Small Wars" his country had conducted against various heathen, savages and rebellious tribes. It is full of tactical theories, battlefield aphorisms and, above all, the arrogance and hubris of Imperial Britain toward the "lesser races" of mankind.

I found that a bit strange inasmuch as the colonel's wisdom about "small wars" was derived in large part from military disasters Britain had suffered in exotic corners of the world. The "wogs" of that era often refused to scamper away like guinea hens; they behaved, instead, like the Sioux at the Little Big Horn.

Still, the "wog" syndrome persisted. We took it into the war against the "little yellow men" of Japan and into the war against the "slants" in Indochina. The British, I strongly suspect, have taken it into the war with the Argentines. It was going to be a "walkover," one of the British commanders observed some weeks ago. Why? Well, because the "Argies" aren't like us, you know.

As the body count rises and as it becomes obvious that not even "Argies" use rubber bullets these days, there will be recriminations and a reexamination in Britain and in the United States of the assumptions that went into the Falkland Islands affair.

The first assumption was that it would be an easy and perhaps a bloodless victory. That was reflected in the jingoism of the popular press and in curious public opinion polls revealing overwhelming support for the recapture of the Falklands and an overwhelming reluctance to spend British lives in the process. The contradiction is easily explained: "Argies won't fight."

This assumption is also reflected in the quick British decision to remove major elements of the fleet from its primary mission as NATO's antisubmarine shield in the North Atlantic. No problem. The fleet soon will be back on station -- presumably intact. That was before the frigate Sheffield went down and before the damage sustained in the landing this weekend.

It also followed from this assumption that a British disaster in the South Atlantic was inconceivable. That is one reason Alexander Haig was beat around the head and shoulders by editorial writers for trying to mediate a peaceful solution to the problem. Why is he wasting his time on the "Argies"? They are bad guys. Let the Brits get after them with our blessing."Argies" won't fight.

The American military, it must be said, never shared that assumption. Our majors and colonels and generals have been saying all along that this could be a costly adventure. And then what ?

Suppose the British carriers are taken off the board and Britain's troops are stranded with the sheep and kelpers in the South Atlantic. Who extricates them? One assumes that President Reagan's telephone will ring. The debate in Washington at that time will be delicious.

That is the trouble with "wogs" and small wars, as Col. Callwell complained in his tome. They are so damned unpredictable, so damned uncivilized.