A black-oriented cable television service today announced plans to offer six hours a week of "urban contemporary" music video, in efforts to capitalize on criticism that MTV, the popular rock video service, shuns black performers.

Robert L. Johnson, president of Black Entertainment Television (BET), a Washington-based cable service with 4.1 million subscribers, announced the new venture at the annual convention here of the National Cable Television Association.

Black and other minority group entertainers have been sharply critical of MTV, a 24-hour Warner-Amex Cable service with 12 million subscribers, for its failure to show the video work of entertainers that do not fit a middle-of-the-road audience pattern.

In his announcement, Johnson refused to criticize MTV. "If a network chooses to target an audience that is their choice," Johnson said. "Cable television offers the diversity of specialized programming."

Johnson said the BET show, to be called "Video Soul," will offer clips, particularly of black performers "who want access to a national video outlet that can serve as a primary vehicle to promote black music videos." He described the music to be featured as "any and all music clips from country to soul that we feel would appeal to a contemporary urban audience."

The tapes used by music video services are provided and produced by record companies. Johnson said BET has sent letters to all major record companies to begin soliciting existing tapes and to encourage the companies to step up production of black videos.

The show will air from 9 p.m. to 11 p.m. Mondays, Wednesdays and Fridays. The program also will include interviews, concerts and music industry news.

Both services are supported by advertising. Johnson said the new video music show on BET would fill 10 minutes each hour with ads. BET's efforts to reach urban audiences have been slowed by the costs and political delays involved in building cable franchises in major urban areas.