The Chicago White Sox fired Manager Tony LaRussa, team vice president Ken (Hawk) Harrelson said yesterday, six weeks after management grudgingly gave LaRussa a vote of confidence.

Third base coach Doug Rader was named interim manager. Rader, 41, formerly managed the Texas Rangers and was hired by the White Sox before the start of the season.

There was no word on a permanent replacement for LaRussa, although speculation has focused on Jim Fregosi, a former manager of the California Angels now managing at Class AAA Louisville. But Fregosi told The Associated Press yesterday that he had not been contacted by White Sox officials.

Harrelson also fired pitching coach Dave Duncan, who will be replaced by Dick Bosman of the White Sox' AAA club in Buffalo.

LaRussa was fired with the team in the midst of a slump. Earlier yesterday, his wife, Elaine, said in a telephone interview that he had called her at their Sarasota, Fla., home with the news. "Managers are hired to be fired. Tony knew that," she said. "But there's a right way to do things and a wrong way."

Harrelson notified LaRussa of his firing Thursday night, ending the tenure of the American League's second-longest surviving manager behind Detroit's Sparky Anderson . . .

Heisman Trophy winner Bo Jackson will shun pro football and sign with baseball's Kansas City Royals, it was reported last night. Jackson, the No. 1 pick in the NFL draft by the Tampa Bay Buccaneers, said he would announce his decision today.

A Memphis radio station, WLVS, said that Royals part owner Ewing Kaufman emerged from a meeting in Memphis yesterday and told a switchboard operator not to return any calls to the media because "we've signed Bo and will announce it today ."

The station said Jackson was signed yesterday afternoon and champagne corks were popped in part owner Avron Fogelman's office in Memphis.