Viacom, the owner of BET, is forming a new cable television channel for middle-aged African-Americans, heightening the competition for the minority viewing audience.

The channel, to be named Centric and scheduled to make its debut in October, will be formally announced at an event for advertisers Thursday night. Centric will complement BET, executives say, by appealing to an older and more affluent audience.

The 29-year-old BET, available in 89 million homes, is the dominant network for black audiences. It attracts roughly four times as many viewers as TV One, its main competitor, which is owned by Comcast and Radio One and available in about 47 million homes. BET, with its reality shows, movies and music videos, primarily draws a teenage and young adult audience.

Cable channel start-ups are rare. With hundreds of channels already in operation, new ones often struggle to earn a spot on cable lineups, but Viacom said it would be able to assemble 45 million homes for the premiere of Centric.

Viacom executives would not comment on whether BET J, a small music-oriented offshoot of the network, would be affected by the formation of Centric.

As Viacom considered the 25- to 54-year-old target demographic for Centric, it realized that “a perfect example would be” Barack and Michelle Obama, said Scott Mills, the president of BET.

Centric will be operated jointly by the BET and MTV Networks divisions of Viacom. Viacom’s channels include Nickelodeon and MTV. Doug Creutz, an analyst for Cowen & Company, called the niche strategy valid but incremental. “They’re not going to hit any home runs doing this, but it can grow their reach over time,” he said.

Mr. Creutz said the African-American adult audience had “been underserved,” and pointed to the series of successful movies by Tyler Perry as evidence that “there’s money to be made at targeting that audience.”