ABC gambled on "Roots" and the bet paid off. The 12-hour dramatization of Alex Haley's book, presented in eight episodes on consecutive nights, was more than a ratings block-buster. It probably will change - as nothing before it has - the manner in which television programming is presented to us.

Television is an instrument of time, as a newspaper is an instrument of space. Time on television is divided into half-hour, hour, 90-minute and two- or three-hour blocks. A comedy series is on for half an hour, a variety show or a detective show for an hour, once a night, once a week. Each show is on when we expect it to be, it is over when we expect it to be over, and we wait for it to appear the following week.

The effect of what we have seen on these various blocks of time varies. Some have a profound effect, some not so profound. We have seen a block of time into which planning, programming and commercials were poured and we have not been touched or moved at all. We have simply used up a block of time.

It is, in some ways, an electronic substitute for daydreaming. The important difference is that the television set supplies the images that in private reverie we supply to ourselves.

But electronic daydreaming and private daydreaming have this in common - both are episodic. They last for a fragment of time. They come and they go and we move on to other efforts as we seek what Graham Greene has called the chief aim of life - the necessity to avoid boredom.

"Roots" was a different use of time. After the first episode was over, we began to arrange our future time - if one can believe the things one heard from offspring, friends, colleagues - so that we could see the succeeding episodes as they unfolded over a compressed period of eight nights.

It is very rare that we arrange our lives in so dedicated a manner around television scheduling. It is true that we may save certain hours, certain nights or certain days for shows and events we do not wish to miss. The weekend football game has become an institution.

But never before in television's short history have so many millions of viewers rearranged their daily lives and their use of time to avoid missing a continuing program that had obviously moved and touched them in complex and compelling ways.

My guess is that nearly all of them felt a profound sense of deprivation when "Roots" ended last Sunday night. And I would further hazard that they are going to find something profoundly absent from their lives when they return to their usual sense of television time use - the situation comedies, detective programs, variety shows, sports and the rest of the electronic daydreams that are served up to us from dawn until well past midnight.

The people who watched "Roots" last week, who rearranged their use of time to satisfy some complex sense of emotional need, are probably asking themselves at this very moment why they cannot have more programming that ranscends television's fixation with chopping up narrative into tidy little packages of half-hour, hour, 90-minute or two-hour duration that are spaced a week apart.

There is no reason why viewers cannot have more of this kind of continuous programming which encapsulates a profound emotional experience into a finite amount of time - a week or 10 days or whatever time it takes to give a story a beginning, a middle and an end.

That is the worst charge that can be made against television, namely, that it chops up our sense of time into fragments that deprive us of a sense of continuity about ourselves and others.

"Roots" did not do that to us. We had, as we watched it, that elusive and procious sense of continuity about ourselves and others that television seems to promise, but usually denies us. That is why I think it has created a hunger in all of us for more program like it.

Those programs will come. It will take some time. But time is what television is all about. The manner in which "Roots" was presented to us demonstrated that time need not be flashed by us in mindless fragments.