This is the week in which the future of Afghanistan is supposed to come up on the international agenda. The meeting place is (as usual) Geneva, Switzerland. And the scheduled principals are Pakistan (up to a point a client state of the United States) and the ''government'' of Afghanistan (in every respect a client creation of the Soviet Union). So it is not unrealistic to say that the United States and the Soviet Union are scheduled in the next few days to decide the fate of Afghanistan.

In the reports one reads on the frame of mind of the mujaheddin -- they are the Afghan patriots who have resisted the Soviet colossus with the help, in different forms, of Iran, Pakistan, China and the United States -- insufficient attention is given to what it is that the Soviet Union has done to Afghanistan during the past eight years. In such cases analogies are useful.

Let us suppose that a huge amphibious operation against a relatively unarmed United States had been initiated simultaneously on our Pacific and Atlantic seaboards. In the course of eight years the aggressors (let us call them the Huts) had killed 25 million Americans and had caused another 50 million Americans to flee to Canada and Mexico, whence they waged their war of resistance. Washington was quickly taken over by the Huts and a stooge installed, who declared himself the head of the government of the United States.

After eight years, the Huts find themselves marginally overpreoccupied with the war against the United States, which in any event imposes on them a diplomatic overhead that gets in their way in dealing with other issues. So they propose to ''pull out'' from the United States. But they want certain reassurances that they find altogether reasonable. The first is that the government in Washington should be a ''coalition'' government that is heavily pro-Hut. The second is that during the change in scene, none of the powers that had been helping American resistance via Canada and Mexico should continue to do so. That assistance must stop immediately.

The American resistance headquarters responds that it is not interested in a coalition government with a power that murdered 25 million Americans and drove another 50 million abroad. But the resistance finds itself facing huge, solemn diplomatic faces representing this and that international interest and insisting that the time has really come to be reasonable about the Huts' little American adventure -- that, after all, the Huts' willingness to withdraw their armed forces from America is a sign of good faith.

The very best roundup on the Afghan scene recently published is by Lally Weymouth in The Post. All the relevant arguments are there, and she has talked with representatives from Iran, from Pakistan, from the mujaheddin and -- most significantly, because it is most frequently ignored -- from China.

''Although President Zia {of Pakistan} is often portrayed as a hard-liner,'' she writes, ''Chinese officials and analysts take an even tougher position -- skeptical of Soviet intentions to withdraw from Afghanistan and convinced that increased aid to the resistance is the key to removing the Soviets from Afghanistan. Chinese defense analysts at the Beijing Institute of Strategic Studies express doubt that the Soviets are sincere in their stated intention to withdraw from Afghanistan. 'The Soviet condition is that the United States and other countries stop interference,' says one expert. 'For the United States and China to cut off the resistance is a condition that must not be accepted.' ''

But in our autohypnosis in scrambling foreign policy priorities, we seem to care more about proving to the Soviet Union that we trust their protestations of perestroika than we do about persuading the Afghans that we consider the murder of one-tenth of their population and the exile of one-third of it as on the dark side of an offense that warrants a ticket for double-parking. The very idea that we should elect this moment -- of all moments -- even to consider letting up on the military pressures that have caused the Soviet Union even to consider withdrawal suggests a collapse in our capacity to think good, rationalist, rectilinear thought.

Our position on the Soviet Union should be a) that it should withdraw all its forces and be satisfied with qualified amnesty for its brummagem Afghan ''diplomats'' and b) that Afghan claims for $70 billion (a figure most recently cited as roughly appropriate) for reparations should be pressed by all the relevant agencies, diplomatic, economic and political, as a modest compensation for Soviet genocide.

Never cut off the enemy's line of retreat, Machiavelli taught us. But that is different from any counsel that you, rather than the enemy, should retreat.