IT IS FORGIVABLE that old imperialist memories should stir in my blood these days. Every English schoolboy of my generation had names like Kabul and the Khyber Pass and Kandahar on his lips almost from the cradle.

For almost a century, British troops sat on the Northwest Frontier of India, to which Afghanistan was the key, facing the Russians. It was the business of empire, in the most romantic of settings. Perhaps the atmosphere of those days is caught in a single name. When the young Winston Churchill joined the Malakand Field Force, his commanding officer was called no less than Sir Bindon Blood.

But the business was serious. Not just to face the Russians, but to face down the Russians. There the two great empires of Britain and Russia were locked in an endless duel, while in Europe and the Middle East they kept the peace with each other. One reason that Britain was involved in Afghanistan -- such are the ways of empire -- was to keep Russia out of the Dardanelles. Even after the Russian Revolution, as late as 1919, Britain marched a whole army into Afghanistan. It was no more inclined to trust the Bolsheviks than it had the czars. Say what one will, empire had its reasons.

But is not quite like that now, although some may wish that it was. Worried and hurried men from the State Department, fresh from their atlases, snatch a bite at the Metropolitan Club and say darkly, "I may be away for a few weeks." But there is no Northwest Frontier Province for them to go to; America has no borders with Afghanistan; where is the solid ground on which to build a long-term strategy?

Presidential candidates who bear no responsibility -- and have precious little sense of it -- may make their easy criticisms. But it must be very frustrating to conduct the business of empire -- keeping the peace around the world -- and to have no firm territory of empire from which to operate. One gazes at Russia's borders with Iran and Afghanistan and wonders what America's planes and ships are meant to do.

Everything has changed, then, except for Russia. The fact of Russia. The permanence of Russia. The drive of Russia. Not communist Russia, but age-old Russia. Not the Soviet Union, but Mother Russia.

There is a great danger now that American policy will be confused, exactly as it was during the Cold War, by thinking that the threat lies in communism and not just in Russia. Communism as such may be useful to Russia as an ideological mask, but there is not the slightest evidence that it has any long-lasting appeal to any people who are free to choose, who are not directly subjugated to Russian might in one form or another.

It is exactly 500 years since Ivan III in 1480 wrestled the independence of Muscovy from the Mongols, and since then no czar or communist in the Kremlin has ever relaxed the Russian drive for expansion. They have waited, yes, but not relaxed.

"In the immensity of Russia," Catherine the Great once wrote to Voltaire, "a year is but a day." And again to Voltaire of her war against the Turks: "We are at war, it is true; but that is an old occupation for Russia, which emerges from every struggle more flourishing than before."

The Russia which boasted that it was the Third Rome -- after the fall of Rome itself and then of Constantinople -- became in our time the Russia that led the Third International. Always it has driven, when it can, west into Europe, south into the Middle East, east into Asia. Where it has found its way blocked in one direction, it has merely turned to look in another.

Obsessed by communism and not concerned with the fact of Russia, America in the 1960s began to notice only the weakness of communism. It became the conventional orthodoxy to point out that communism was no longer monolithic, and the fact that Russia was as monolithic as it had been for 500 years was overlooked. What is happening to America now in the events in Afghanistan is that none too soon it is rediscovering the Russia to which a year is but a day.

President Carter will probably pay dearly for his characteristically candid admission that he has revised his notion of Russia during the past few weeks, but many who will batter him for such ingenousness will in fact be retrieving ground of their own with considerable less frankness.

Not least does one wait to hear from the revisionist historians of the Cold War. They did a great deal of damage by purporting to show that Russia from 1944 to 1949 had no expansionist aims at all. Far from wanting to expand, it was insecure and fearful. If only we had understood that Stalin was really a rather cuddly but anxious old man, then we would have realized that he did not trample Eastern Europe underfoot out of agression. It was these revisionists who gave detente its intellectual paraphernalia.

As other historians have pointed out, they made, at best, naive and, at worst, dishonest use of the evidence. But this is not the place to bother with their methods. What matters to us is that those who were responsible for American policy at the time -- George C. Marshall and Dean Acheson, and of course the president they served -- anticipated such poppycock and judged Russia by its own actions. The Russia still of all the Ivans.

Acheson was luminous in his descriptions of the policy by which America then checked the expansion of Russia. To read today his many speeches and endless testimony before Congress is like a breath of fresh air, after the smog in which America's attitudes to Russia have been wrapped for two decades. Moreover, he directly faced the question of what America can do without a territorial empire from which to resist.

What concerned him were the "situations of weakness" in the world. "Every time one of these situation exists -- and they exist in Asia, and they exist in Europe -- it is not only an invitation to the Soviet government to fish in troubled waters. To ask them not to fish, and to say that we will have an agreement that you don't fish, is like trying to deal with a force of nature. Therefore we go to work to change these situations of weakness so that they won't create the opportunities for fishing."

This is very like Henry Jackson's comparison of Russia with a hotel burglar. It goes down the corridor trying all the doors. If it finds a door locked, it leaves it alone. But if it finds a door open, it goes in and takes what it wants. It is no different now from 30 or 500 years ago.

Acheson would be appalled today at the number of "situations of weakness" in the world, the fault of no single president and no one party in the past two decades. The hotel burglar has never had it more easy than now. In place of the territorial empire which America does not and cannot possess, he and others substituted the grand alliances of which America would be and be seen to be the leader.

To be the leader of an alliance is not the happiest of positions. The leader must prove itself to be constantly reliable, while the lesser allies are allowed to be truculent and feckless. But even in these circumstances it is the reliability of the leader that is the key. "We are in a situation where we are playing for keeps," said Acheson, and that is exactly all that the dependent allies want to know.

If one looks at more than the armaments that are required, and the willingness to use them, one may see in America much that makes a leader seem unreliable. A nation which in a fit of self-indulgent pique sets out willfully to destroy its intelligence operations is not going to be much trusted by its allied governments. They expect its intelligence agencies to protect them. Equally a nation whose Congress irresponsibly decides what military aid its allies may receive -- Turkey one day, Pakistan the next -- is not a nation which those allies will believe is playing for keeps.

To say that America is playing for keeps is only the reverse of saying that in Russia a year is a day. "Historically the Russians state has displayed considerable caution in carrying out these drives," said Acheson. "The Russian leaders like to bet on suc things. Russian policy makers, czarist or communist, have always taken a very long view." It is America's own long view in response which needs to be reestablished in its present reawakening.

Whether one agreed with Acheson or John Foster Dulles or not, one of their virtues was that they made foreign policy a subject of a great debate. America knew what it was doing and why. But with the exception of the relatively marginal issue of the war in Vietnam -- for such, in the long view, it was -- there has been no great debate on foreign policy in America since the early 1960s.

It seems to me that it will be a tragedy if now that the opportunity is there, it will be distracted and confused, not only by the election, but by what really are side issues, such as giving hospitality to the shah, or even the ultimate fate of the hostages. These are not much in the long run.

Let us return 60 years, to where we began. When the British threw an army into Afghanistan in 1919, they also proclaimed a protectorate over what is now Iran, and in effect seized the right to mandates over what are now Israel and Jordan and Iraq, and so established themselves from the Mediterranean to India, which they happened also to have under their belt; in fact, over the whole area that is now in turmoil.

It was a last absurd fling of territorial empire. Britain very quickly withdrew from Afghanistan and, lo and behold, American and French protests, forced it to withdraw from Iran. But at least the British had some idea of the unity of the vast area, with Russia lying along the whole stretch of its northern border.

For behind it all lies one vast question that has yet to be answered. America is a nation which in effect is bounded by two oceans. Russia is a huge land power that stretches across two vital continents. Britian may also have been a sea power, but in the days of empire it could make itself a land power as well. The question which America has to settle is: What can its planes and ships do with no empire on land?

That ought to be the measure of the debate.