Inside Report (4)

Why hasn't the Soviet Union mounted a more forceful response to the Israeli invasion of Lebanon?

Reagan administration analysts are split on the question. Some think the Soviets are not really capable of mounting an adequate response, through the resupply of military equipment to Syria, and are too cautious at this point to want to back up Syria with Soviet troops. The Soviets leadership is in the midst of a transition period, and most analysts think this makes for caution.

Some analysts, on the other hand, think the Soviets count on profiting eventually from a ''radicalization'' of Arab nations, a development which they expect to result from the Israeli invasion. But for the time being, Soviet weapons and training seem to have suffered a loss of credibility in the eyes of many Arabs.

Defense Department officials say that if they had to replace what the Soviet-supplied Syrians lost in planes, missiles, tanks, and trucks with the equivalent in American equipment, the bill would run upwards of $4 billion US dollars.