Because the Soviet Army miscalculated and underestimated the challenge it faced in Afghanistan, it failed to defeat inferior forces scattered in the mountainous country, U.S. intelligence analysts say.

The Red Army's failure resulted from a troop strength that was too small, a command structure that was overcentralized and an Afghan power base that was too scattered, sources said.The experts said the United States capitalized on the 8-year-old Afghan war to obtain invaluable intelligence about Soviet weapons by employing teams of Pakistani and Chinese nationals or British mercenaries to retrieve components of systems partially destroyed by the Moslem rebels in Afghanistan.

"The United States obtained invaluable knowledge of Soviet Army operations, strategy and tactics" by careful study of the Soviets' war with the guerrillas, one State Department official said.

Analysts said the Soviets badly miscalculated the task they faced.

Phil Karber, a Washington expert on Soviet tactics, said the Soviets first sent in battalion-sized airborne units to secure routes of advance, key air bases and the capital of Kabul when the invasion began in December 1979.

A U.S. intelligence expert said the Soviets were surprised to find that holding Kabul "meant holding next to nothing, since power was based in tribes and villages widely dispersed in the countryside."

Afghanistan is the size of Texas but its various tribes speak 23 different languages, State Department officials said.

Another problem was that Afghan-speaking Russian troops began to desert and had to be replaced with more reliable Soviets from non-Asian areas of the USSR, Pentagon officials said.

One Pentagon analyst said these troops "were not as able to endure hardship" as the rebels, placing the Soviets at a disadvantage."Basically, the Russians are a western army," the analyst said.

He said the Soviets began to use Afghan troops for most of the ground operations to avoid casualties, but that tactic created a "convoy mentality" in which Soviets forces grew reluctant to leave their vehicles for combat.

"At bottom, the fault lay with a command that sent representatives from Moscow to lead operations and which allowed very little initiative to local commanders," said David Isby, a Washington attorney and expert on Afghanistan.