One bummer after another for the Cincinnati Bengals, now Ross Browner and Pete Johnson testifying to frequent purchases of cocaine--in a span that began in August 1980 and encompassed that (AFC) championship 1981 season.

Defensive end Browner and fullback Johnson--federal and team officials said they are the only Bengals involved--were given "informal immunity" by the government for being prosecution witnesses in U.S. District Court, Cincinnati. They may not be so immune from National Football League action.

The two said they bought the stuff, about a gram at a time for $80 or so, about 15 times apiece from one John F. Schultz, 35, a plumber on trial for 20 counts of trafficking. The league says it is investigating the players.

Mike Brown, the Paul Brown son who is Bengals' general manager, said the club notified the NFL of the revelations, will await results of its investigation, and "if sanction is required, it'll be administered."

The Bengals already faced loss of Dan Ross and Cris Collinsworth to USFL in 1984 and '85, respectively, and now hear Coach Forrest Gregg: "Wonderful, isn't it. We've had no good news at all. I'll be glad when the offseason is over."

Johnson said he just "tried" cocaine "off and on for about a month, that's it," and never before a game. "I don't think anyone can use anything during a season and play a season" . . .

At Johnson's old school, Ohio State, No. 1 quarterback Mike Tomczak has back the eligibility he lost recently after his photo appeared in a clothing ad. The NCAA reinstates him because the $40 fee he received went to charity; besides, the ad didn't identify him as an athlete . . . Reggie McKenzie, last of the Buffalo Bills' "Electric Company" offensive line that led O.J. Simpson through his record 1973 year, has been dealt to his old coach, Chuck Knox, and the Seattle Seahawks for undisclosed draft picks . . . Ed Garvey, the former NFLPA director, has settled into his job as Wisconsin deputy attorney general and is living with his boss, Bronson La Follette, until he can sell his house in Chevy Chase and get his wife and three daughters moved to the Madison area . . . A Chicago real estate developer, Walter Kaiser, says he may establish an International Football League team in Milwaukee--"the league has given me a franchise, they needed a 12th team." Details about IFL, another (!) spring (!) league, are to be announced Thursday in New York.