Despite new evidence showing popular resistance to the Soviet invasion of Afghanistan far beyond anything anticipated by Moscow, the widening split in the Western alliance is making it difficult for President Carter to exploit what ought to be an opportunity against the Kremlin.

The evidence is clear: rapid disintegration and unreliability of the Soviet-controlled Afghan army, assassination of Soviet and pro-Soviet officials, rising Russian casualties.

But Western Europe -- especially France and West Germany -- shows no liking for any muscled response to the December 1979 invasion despite storng pressure from Carter. Thus, the Kremlin can bide its time in achieving control over 15 million Afghans. There is nothing standing in the way.

"A major benefit for Moscow is discovering they can do this Afghan invasion without the Europeans rising up," one administration official told us. "That quite a discovery."

President Carter had to beg, cajole and genuflect to win even the marginally thin support he has gained from America's NATO allies. Only West Germany has boycotted the Moscow Olympics, and none of the Europeans likes Carter's effort to block sophisticated industrial equipment for the Russians.

Carter's own response to the invasion was mild enough, particularly in view of his hot rhetoric. But at least the president was realistic enough to withdraw his cherished Strategic Arms Limitation Treaty from the Senate and, in effect, to decree a temporary end to dentente.

In contrast, his allies want to shrug off the invasion as of no real concern and get about their money-making business of even more trade with the East. But now, considering the continued political and military resistance in Afghanistan, is the time to press Western demands to get out. Carter knows that the European "cover" position -- that the Kremlin can soon be persuaded to let Afghanistan revert to its historic neutrality -- is fradulent.

That leaves hin in a different position to handle the most devasting setback to the West thus far in his administrtion. Without the full, aggressive support of Western Europe, Carter's policy is stuck on dead center. Considering what is actually happening on the ground in Afghanistan, This may be the last moment -- and certainly the most advantageous time -- to compel the Russians to cease and desist.

The Soviet efforts to control the disintegrating Afghan army is less difficult than coping with the split within the controlling Communist Party. One administration report claims that "if the present uneasy truce" between the two feuding factions continues, "there could be another major upheaval," ending all pretense that an Afghan government exists.

In fact, it does not exist. Administration officials are now "completely subservient and responsive" to Soviet ambassadors in each capital of the world.

It is no wonder, then that Kremlin planning today does not even contemplate any future withdrawal from Afghanistan: if the Russians went home, anti-Soviet insurrection would take over. To counter this, the Soviet occupiers are trying to brainwash Afghan youth with new Soviet-style textbooks, molding education to fit Moscow's view of history in hope of building a pro-Soviet generation for the future.

Evidence that the Russians are digging in for the long haul is pervasive: the first Soviet railroad to Kabul is being constructed; two permanent bridges are replacing the pontoons that carried Soviet troops into their bloody invasion over the river along the Soviet-Afghan border; the tour of duty of Soviet troops in Afghanistan has just been extended to two years; fuel storage bladders are being replaced by extensive underground storage facilities.

Tapi Tajbek Palace, where Soviet gunmen assassinated President Amin Dec. 29 as the invasion hit high gear, is being cleaned up and renovated. The new occupant of this historic Afghan treasure: a Soviet command headquarters to run the country.

Carter administration officials discount reports that a major reinforcement of the 85,000 Soviet troops fighting in Afghanistan is about to occur. With the West split in its response to the first case of military aggression outside the Warsaw Pact since World War II, the Kremlin can proceed slowly. It wants no bad headlines until the Olympics have finished celebrating the just and peacful nature of Soviet foreign policy.

In truth, Soviet subjugation of Afghanistan, slow or fast, would have been impossible against a West that was united, militarily prepared and armed with a common strategy for dealing with the Russians. Since none of those three conditions exist, it matters little whether Moscow encounters times in Afghanistan, a fact of utmost gravity in the struggle for world preeminence.