As long as Soviet invaders kept up their bloody occupation of Afghanistan, Americans paid close and critical attention to what was happening there.

But that attention has waned following the departure of Soviet troops in mid-February. Too many Americans assumed that the puppet government of President Najibullah would collapse shortly after the Russian pullout. That assumption, tragically, has proved to be way off base.Just how far off can be seen from the fact that the Najibullah regime still holds about as much power and territory as it ever did despite almost daily rocket attacks on the government-held capital of Kabul and repeated guerrilla forays elsewhere.

One reason the regime in Kabul has not toppled is that the rebels keep fighting themselves as well as the Soviet-backed government. Only a few days ago, gunmen from an extremist rebel faction assassinated 30 key officers and commanders of a more moderate rebel group.

But the main reason the rebels have not yet triumphed is that the Soviet Union seems to be much better at fighting wars by proxy than the United States is.

By one official estimate from Washington, Moscow has not only maintained but even increased the flow of weapons to Kabul since February even though the Soviet economy is a shambles. Each month, Kabul is said to be getting between $200 million to $300 million worth of Soviet supplies. By contrast, the rebels were getting no more than $50 million worth of help a month from Washington even when U.S. aid was at its peak.

Contrary to what most Americans seem to think, the Free World did not win the war in Afghanistan just because Soviet troops withdrew. The struggle to bring independence to Afghanistan is still going on with a vengeance. Afghan patriots are still eager to kick out the puppet regime. If this cause is to triumph, Washington and its allies must do more to help.