Pakistani writer Mushahid Hussain, in his article "Eyewitness in Mecca" {op-ed, Aug. 20}, relates some little-known details about the preconditions agreed upon between Saudi officials and the Iranian organizers of the July 31 "political demonstration" that went awry and led to the bloody massacre of hundreds of Iranian "pilgrims." I found those details alarming.

Mr. Hussain tells of the Iranians' surprise at the tough Saudi reaction and intervention, when the Iranians tried to exceed the agreed-upon terms and limitations, thus threatening Saudi sovereignty within its own national borders. But Westerners, and Americans in particular, can take little comfort from the Saudi response, which was dictated by the Saudis' own narrow interests.

If we examine the agreed-upon preconditions, it is chilling to note that the Saudi officials had apparently voiced no objection to the burning of three American flags by the Iranian demonstrators or the carrying of banners denouncing the "three satans," America, Russia and Israel.

Equally chilling, if we will take a moment to analyze its long-range implications, is the fact that among the fundamentalist Iranian demonstrators marched a contingent of Afghan mujaheddin -- representatives of those same rebel forces currently being armed with highly sophisticated American weaponry with which to shoot down Soviet aircraft over Afghanistan.

Will this weaponry one day be turned against our own aircraft as well? The possibility is not too far-fetched, alas, if Iranian fundamentalism, drawing on the combined resources and lust for power of all of the Moslem states in the region, were to mobilize its huge pool of fanatic forces in a future Armageddon designed to destroy the "infidel" civilizations of both West and East and to rule the world in the name of Allah. They just might catch us by surprise, as we lie sleeping.

Rather than proposing the sale of a billion dollars' worth of armaments to the Saudi rulers, would we not do better to start mending our fences with the Soviets?

W. H. CHURCH Charlottesville