"THERE IS only one Berlin" -- President Reagan's words at The Wall Friday -- may not have quite the zing of the JFK original "I am a Berliner." But Reagan did move the Kennedy declaration out of the realm of compassion and into possible politics and very possible grave danger in his implied plea for the reunification of Berlin, and then, as night the day, all Germany.

Many, perhaps most, Americans think of "divided Germany" as a kind of tragedy inflicted upon our most reliable allies, the Germans, by our most feared and hated enemy, the Soviet Union. It is thought, too, that Germany of right and custom, like other countries, ought to be unified, to be one country with one capital of more plausible claim to world-class status than provincial Bonn.

Meanwhile, many, perhaps most, Americans think that the reason we have not fought the Soviet Union in World War III is that we are amassing huge amounts of arms. And if we were not amassing huge amounts of arms the Russians would be on Staten Island tomorrow. The proof is that 42 years have passed without World War III's having started.

But one possibility that doesn't get talked about much is that the heart of Europe, Germany, was divided as the result of that country's last effort to subjugate all non-Germans within reach and has remained so to this day.

Divided Germany or arms buildup -- who can say which is the likelier reason? All one can say is that never in the history of humanity has a huge arms buildup ever led to anything but war. And, on the otherhand, never has German unification ever been achieved by or led to anything but war. In fact, the history of Germany as a state -- a remarkably short history -- ought to give anyone pause when advocating or even thinking about the reunion of the two parts of the divided Germany.

Before 1871, the closest thing to a pan-Germanic state was the Holy Roman Empire, which was, in the classic description, "neither holy, nor Roman, nor an empire." It included large pieces of France and Italy and left out what became the most important part of the real German Empire, Prussia.

Germany's history begins with Otto von Bismarck, the "Iron Chancellor" of Prussia and then of Imperial Germany, which he largely created. Early in his career of transforming Prussia into Germany -- and vice versa -- he appeared before the Prussian House of Deputies and unveiled a policy of "blood and iron." The iron turned out to be that of the Krupp family, at considerable gain to that family, the blood that of some generations of Germany's young men, at their loss.

In 1864, two years after his "blood and iron" formulation, Bismarck's Prussians invaded Denmark and seized the border provices of Schleswig and Holstein under joint occupation with Austria.

In 1867, the Prussians invaded Austria to settle a dispute over the joint occupation of the Danish provinces, ended up with sole occupation and with Austria out of the running as unifier of a new Germany.

And in 1870, the big one, Bismarck easily maneuvered France's preposterous emperor, Louis-Napoleon, into a war that ended with France humiliated, and the king of Prussia the emperor of a unified Germany.

Less than half a century after unification, the new Germany launched World War I, "The Great War," against Serbia, Russia, France, Britain and most of the rest of Europe except for its fellow German Empire, Austria. The Germans lost this one but managed to destroy both the Austrian Empire and the Russian European Empire, as well as their own, helping Lenin and his Bolsheviks to take over Russia.

Twenty years after that one, the still unified Germany invaded and occupied Czechoslovakia, Austria, Poland, Holland, Belgium, Denmark, Norway, France, Yugoslavia, Hungary, Bulgaria, Albania, Greece, Roumania, and large parts of North Africa and the Soviet Union.

But the Germans lost again and this time the victorious allies had the good sense to divide Germany into four occupied zones. The arrangement was meant to be temporary and on paper, at least, it was. The zones occupied by Britain, France and the United States eventually were formed into West Germany. The new country became and has remained an ally of the West, with many Americans regarding it as our best bet in Europe. The Soviet zone, too, formed into a people's republic allied with the Soviet Union. Both Germanies would like reunion, but each on its own terms.

Granted all those well-known facts, it is hard to see how anyone can seriously contemplate the reunion of the two Germanies as something likely to happen any time soon. And even if it could, it is not clear that it ought to, or that we should take the chance of finding out what it might bring about.

In discussing any such theory it should be enthusiastically acknowledged that in so many ways, the Germans are marvelous people. We are all in their debt. In places like the Kennedy Center's Concert Hall, the three B's -- Beethoven, Bach and Brahms -- all German, dominate as they always have. Their literature gives us Luther, Mann, Goethe, Schiller and Heine.

All this and much more is true. It's just that, considered as a unified nation, in a world parched for peace, the Germans are not quite ready for self-government.

Frank Getlein, an editorial writer and political columnist for the Washington Star, is a commentator for National Public Radio.