There is little sense in trying to compare ABC's extraordinary dramatization of Alex Haley's "Roots" to serials like "Rich Man, Poor Man," or to such continuing narratives as "The Forsyte Sage" or "Upstairs, Downstairs."

It is true that "Roots" is not the first serial to deal with the subject of a family and its evolution over an extended period of time. The distinction is that "Roots" deals with a family and its evolution in the context of slavery. That distinction is of major importance, since the introduction of slavery into this country is the continuing central issue of our national existence.

ABC's eight-part, 12-hour presentation of Haley's "Roots: The Sage of an American Family" begins tonight on Channel 7 with a two-hour episode at 9 o'clock. The series concludes next Sunday. Its effect will be heightened by the decision of ABC's Fred Silverman to show the episodes on consecutive nights rather than using the now-conventional approach of one segment a week for eight weeks.

But what makes "Roots" so compellingly unique is that television is finally dealing with the institution of slavery and its effect on succeeding generations of one family in a dramatic form.

That effort has been almost absent from our television screens. I asked several people if they could recall a fairly recent example of slavery examined in a dramatic - as against a documentary - form. The only program recalled was "The Autobiography of Miss Jane Pittman."

All of us watch television with what Walte Lippmann called in "Public Opinion" - published 25 years before the advent of television - "the pictures in our heads." He meant by that the stereotypes that we have of people and places.

We watch detective [WORD ILLEGIBLE] on television with stereotypes of cops and killers, pictures in our heads that we have formed from other television shows, movies or books. We watch science fiction on television with different stereotypes assembled from moon landings, Star Trek and, if you are old enough, Buck Rogers and Flash Gordon.

But we bring to our television screens, for the most part, pictures in our heads about slavery that have been formed by history books, novels and movies. The evening news programs, especially in the '60s, brought us pictures of the consequences of slavery, but not of the institution itself.

This involves one, especially in the opening episode of "Roots," when we are transported in dramatic time back to Gambia, West Africa from 1750 to 1767, in a greater than usual effort of what Coleridge called "the willing suspension of disbelief."

There has already been criticism voiced that the language of the young hero, Kunta Kinte, and members of his tribe, is formal and stilted; that it and the almost lyrical depiction of that culture is false and maudin.

That does this drama a great disservice. We come to the television screen tonight not as cultural anthropologists but as viewers. Most of us have not read the book, which already has sold more than 500,000 copies. We are not seeking historical exactitude, but what this television adaptation provides: a dramatic sense of what the institution of slavery did to one family that endured and survived it.

All of us - blacks and whites - will bring to this drama different perceptions of what the institution of slavery and its consequences have meant to us as a nation.

But what makes this television experience so compelling, so different from anything we have yet seen on television, is the attempt that has been made to achieve a harmonious unity of those perceptions as we become absorbed in the destiny of the individuals that the institution of slavery so traduced. We are watching more than a drama.We are witnessing an experience.

The opening episode begins with the life of Kunta Kinte (LeVar Burton) in his village, his initiation into the rites of manhood, his capture by slave traders and the slave ship that takes him and 139 others to the American colonies. The ship is commanded by a conscience-stricken captain (Ed Asner).

There may be some complaints about the realism of the scenes aboard the slave ship. They are very realistic and they are very grim. But one cannot accuse the people responsible for this television adaptation - David Wolper Productions - of reaching for the sensational. The slave ships were hell holes, and the scenes succeed in approdimating that horror.

Tonight's episode ends with Kunta Kinte aboard the slave ship, bound for Annapolis, in 1767. The story resumes Monday night with an unsuccessful attempt by the slaves to take over the ship. It is followed by the landing in Annapolis and Kunta Kinte being sold to a planter from Spotsylvania County, Va., William Reynolds (Lorne Greene).

He is given the name of Toby by Reynolds and entrusted to the supervision of another slave, Fiddler (Lou Gossett), with instructions to make him a good field hand within six months.

Rebellious and defiant, Kunta Kinte is introduced into the slave life of the South. He tries to escape but is tracked down by hounds and returned to the farm where overseer Ames (Vic Morrow) orders another slave to beat Kunte Kinte until he is willing to say to the other slaves, assembled for the whipping, that his name is no longer Kunta Kinte, that it is Toby.

The second episode ends that way, with Kunta Kinte lying in Fiddler's arms: the young newly arrived African slave, beaten into submission, being wept over by the old American slave, who long ago made his separate peace with the institution of slavery.

Tuesday's episode will find Kunta Kinte/Toby (John Amos) as a grown man in the year 1776, and still rebellious. But his final attempt to escape costs him his right foot. He is nursed back to health by Bell (Madge Sinclair).

In subsequent segments Kunta Kinte/Toby marries Bell and passes up his last chance to escape when the couple have a baby whom they name Kizzy; Kizzy grows up, and as punishment for helping a young slave run away, is sold to a new owner (Chuck Connors), who rapes her; the focus then turns to the child born of that rape, Chicken George (Ben Vereen). Chicken George - his name comes from his skill in training fighting cocks - is sent off to England to pay off a debt his master has incurred, and with the promise that he will return a free man.

Chicken George returns from England in 1859 and is reunited with his family on the eve of the Civil War. By the concluding episode, Chicken George and his family are being threatened by nightriders and carpet-baggers. He decides to move the family from Virginia to Henning, Tenn.

That is not the way Haley's book ended. He went on to describe three succeeding generations. But producer David Wolper decided to end the series at this point with the possibility that if it is a success, the rest of the family history will be dealt with in a sequel.

My guess is that the coming week's episodes will amount to both a great artistic and a ratings success - and that the sequel will be made.