Since "Roots," the question has been asked more and more often: Why isn't there a single dramatic series on TV starring blacks?

In the past year, the response from Hollywood often included vague references to a series in the works for NBC called "Harris and Company." It was to star Bernie Casey as a widower who moved his family from Detroit to Los Angeles in the highly-rated TV movie from last season, "Love Is Not Enough." Casey would be a strong, loving dad for his brood of five, and he would be an independent breadwinner as the co-owner of a gas station and towing business.

It would be a black and blue-collar "Eight Is Not Enough"-if it ever got on the air.

Well, it finally did go on the air March 15. And last night, it went off, probably never to return.

What happened? "HARRIS AND COMPANY" BOMBED. ITS RATINGS WERE TERRIBLE. ITS SECOND AND THIRD EPISODES PLACED LAST ON THE WEEKLY LISTS OF NIELSEN RATINGS FOR PRIME-TIME PROGRAMS.

BUT EXECUTIVE PRODUCER STANLEY ROBERTSON CONTENDS THAT HARDLY ANYONE SAW IT BECAUSE HARDLY ANYONE KNEW IT WAS THERE. HE QUESTIONS WHETHER NBC gave it a fair chance.

NBC had told Robertson that his show would begin last night instead of end. The plan was that "Harris and Company" would be presented on four Thursday nights during the spring rerun season, when the competition wouldn't be so keen, and if it drew an audience it would be picked up for the fall schedule.

NBC Entertainment President Mike Weinblatt had explained the strategy in a letter to Robertson earlier this year.

"You know as well as I do the advantages of a springtime introduction.It worked with 'Family' and 'Eight Is Enough,' two series which were also humanistic family dramas. In our judgement, this kind of program needs to be introduced with great care, and scheduled where it will have a real chance-preferably against repeat programming on the other networks."

At 5:30 p.m. on Friday, March 2, however, Robertson got the word that plans had changed. "Harris and Company" would make its debut on March 15-nine working days later.

Robertson says he was dismayed. This would place his show against first-run episodes of "Mork and Mindy," the hottest series on television, and its highly-rated mate, "Angie," on ABC. On CBS, the competition would be "The Waltons" and "The Chisholms" for two weeks apiece. The former was a veteran ratings winner; many Sunday supplements already were planning to feature the latter on their covers that week.

Robertson and Universal had their own plans for pomoting "Harris and Company" through Sunday supplements, TV Guide, Jet and other publications. But ehese plans were all geared to a premiere date of April 5. They had to be abandoned.

Consequently "Harris and Company" went on with virtually none of the fanfare that often is required for TV fare to attract viewers:

Paul King, NBC's vice president of prime-time series, says the "Harris and Company" air dates were moved up because the show's predecessor in the time slot, "Little Women," was such a failure that it was canceled prematurely. "Harris and Company" was ready to take its place.

"I don't have to tell you how many problems NBC has," says King. "Management had to do something." He sympathizes with Robertson's pique at the fouled-up promotion plans, he says, but he doesn't think the quality of "Harris and Company" was damaged by the final rush job. He would not offer an opinion on what the quality of "Harris and Company" was.

Some of the reviews of the show (like most spring replacements on NBC, it was not available for press preview) thought the characters came off as too goody-goody. Robertson says the first episode was the most "sentimental" of the lot, and that he would gladly work with NBC to toughen the series if the network so desired.

He cites a list of shows that were given time to grow before they became hits, including "All in the Family" and NBC's "Little House on the Prairie." He points out that CBS has stuck by "The Paper Chase" this season, even though it has yet to become a ratings success, because CBS chief William Paley believes in it.

But he doesn't expect the same thing to happen with his show: "I think NBC will say because it didn't do well in the ratings, forget it."

King confirms that likelihood: "My opinion is that is has very little chance (of making the fall schedule)."

Robertson, who is black, said his 9-year-old son asked him the other day "why black kids on TV all seem so silly and disrespectful."

"If the kids of other TV executives asked, 'Daddy, why do white kids on TV seem so silly?" added Robertson, "there might be some changes."