Supreme Court Justice Lewis F. Powell Jr. is in the Mayo Clinic in Rochester, Minn., for surgery to correct a hernia that developed as the result of the removal of a cancerous prostate last January. The 77-year-old associate justice's hernia operation was successful, but it is not known when he will return to Washington . . .

The Los Angeles and Beverly Hills chapters of the NAACP have dissociated from the national organization, which is protesting the hiring practices of black music stars Tina Turner, Michael Jackson, Diana Ross, Lionel Richie and Prince. An NAACP official had accused the entertainers of "hypocritical discrimination" against employing black professionals . . .

Rep. W.G. (Bill) Hefner (D-N.C.), 55, formidable chairman of the House Appropriations subcommittee on military construction, is recovering in the National Hospital for Orthopedics and Rehabilitation in Arlington from a "mild to moderate" heart attack suffered two weeks ago . . .

Up there with all those important icons of our times, the Campbell soup cans, Brillo boxes, Marilyn Monroe and Mick Jagger, will be Pete Rose. The Cincinnati Art Museum has commissioned pop artist Andy Warhol to paint a portrait of the Cincinnati Reds player-manager, who entered yesterday's game 36 hits behind Ty Cobb's all-time hitting record of 4,191. The museum will sell a limited number of Warhol's silk silk-screens that may be done in the fashion of a large baseball card . . .

Madonna's nude photographs are certainly a hot item. Playboy announced in Chicago yesterday that it is beating Penthouse to the newsstands with those sexually explicit pictures of the rock star, and to prove the point produced a copy of the September issue at a press conference. There is also some legal wrangling over just which magazine has the rights to whose pictures. Madonna, who is apparently planning her August wedding to actor Sean Penn, is saying nothing. And in her home town of Bay City, Mich., alas!, Madonna now will not be receiving the key to the city. Bay City Mayor Timothy Sullivan had offered the key as an inducement to get Madonna to visit, but because of all the recent nude photos publicity, feels a key "would not be in good taste." Does anyone really care? . . .