TWENTY YEARS AGO this week, people around the world stood in the twilight or the early dawn to look for that small space satellite that had been rocketed into orbit by the Russians. It was a moment, perhaps the first in history, that was widely and immediately recognized as the beginning of a new era. We can still remember the eerie feeling that came from watching that light move across the sky, knowing that man had put it there and wondering where it could possibly lead.

Given the mood of the 1950s, it is not suprising that this new era was perceived first in terms of military superiority and international prestige. Sputnik conjured up visions of warfare conducted in space, of spacecraft threatening unfriendly nations with monstrous new weapons and of the Soviet Union's using its lead in technology to dominate the world by means of either direct military force or the power created by this type of success.

Sputnik, it turns out, did not lead in that direction. We know now that most of the military uses of space are negative and defensive in nature. The talk of warfare in space now is concerned with the elimination of the intelligence and communications capacities of an enemy; the idea of men fighting men there has yielded to the reality that the human instinct for survival increases enormously in an environment in which the hold on life is so tenuous. Even the prestige and influence the Soviet Union acquired with the first space spectacular were quickly dissipated as Americans answered the challenge.

But Sputnik did lead in other directions. In reaction to it, this country embarked on a spending spree intended to improve the quality of its schools and students. Whether we succeeded or not is still being argued. But the nation did produce a generation of engineers and scientists unmatched by any other in size and skill. Now, the same nation is struggling with the question of how to absorb them and their successors into the labor force. But from these engineers and from the huge federal investment in space programs came a stream of technological advances that altered the quality of daily life - almost everything from food and drink to the slide rule has been touched. And also from those hard-working space experts came an enormous body of knowledge about how people can travel and work in space, knowledge that we do not fully exploit because using it costs too much.

The moon race is history now, and the course on which Sputnik set us has taken another turn. The main space enterprise today is the search for knowledge about the planets, the solar system and the universe. The craft that have gone or will go to Mars, Venus, Jupiter and elsewhere are designed to provide a few more hints about where it all came from, how it all happened and what it all means. There were, of course, some dreamers back in the 1950s who knew that this was where Sputnik would take us eventually.But that point was lost - or almost lost - on most of us in our concern and fear about the harm that might flow from Sputnik and its successors. Twenty years can do wonders for your perspective.