In Black Homes, Some TV Hits Aren’t So Big : Ratings: Once-small differences in viewing tastes have widened in prime-time viewing hours.

Every Tuesday night, millions of households tune to ABC’s “Home Improvement.” In a typical week, the situation comedy about the host of a fix-it show is the most-watched program on the air.

Yet one group of viewers is decidedly sparse among the masses of “Home Improvement” fans. In African American households, the program barely makes the top 30.

Other big network hits are even less popular: “Seinfeld” and “Frasier” don’t even crack the top 90 with blacks despite consistently finishing in the top 10 for viewers as a whole.

The top show for black audiences this season: “Living Single,” a Fox sitcom that ranks 69th among all audiences.

Network executives, as well as advertisers and their agencies, have known for years that blacks and whites have different viewing tastes. But, as the relative popularity of “Home Improvement” and “Living Single” illustrate, these once-small differences have begun to widen into a vast chasm during prime-time viewing hours.

During the 1985-86 season, for example, 15 of the 20 shows most popular among blacks were also top 20 shows among all viewers. By last season, only three programs among the top 20 had “crossover” appeal among both black and non-black households: ABC’s “Monday Night Football,” NBC’s Monday night movies and the comedy “Fresh Prince of Bel Air,” also on NBC.

To some, the racial trends among prime-time audiences are a natural result of a positive trend: the increasing number of network programs created by, for or about blacks. According to BBDO Worldwide Inc., a New York ad agency, there were 25 programs on the four networks with black performers in starring or major roles last year, up from 16 just two years earlier.

“TV was pretty much a white medium for so many years; it was hard to find many black faces,” said Doug Alligood, the BBDO vice president who conducted the agency’s study. “This is a celebration of diversity, and it’s wonderful.”

To others, however, the fragmenting of the audience by race is evidence of increasing cultural separateness.

“Part of it is the general trend of race relations in this country,” said Robert Johnson, chief executive of the Black Entertainment Television Network, which has become a national cable network by targeting black audiences.

“People are a little bit more separate in their racial interaction than they were in the 1970s and ‘80s. People are identifying more with their own culture and ethnicity and feeling comfortable about doing so, without the pressure to integrate or amalgamate cultures,” Johnson said. He added that “that’s not necessarily a bad thing.”