Sport magazine's September issue ranks the Maryland Terrapins as the No. 1 college football team in the nation, the magazine confirmed yesterday.

The Terrapins, who won their second consecutive Atlantic Coast Conference championship last year, finished 9-3 overall and 5-0 in the conference. They defeated Tennessee, 28-27, in the Sun Bowl and ended the season ranked 11th by the Associated Press and 12th by United Press International . . .

There's another Tranquill coaching at Navy. Shirley Tranquill, wife of football Coach Gary Tranquill, is the coach of Navy's women's gymnastics team, which has been elevated from a club sport to varsity status for the 1986 season.

Shirley Tranquill, who worked with the club team last year, also coaches a private club team and will be a judge at the National Sports Festival at Baton Rouge, La., in July.

She has tutored several private gymnastics club teams, including the Aerial Port Gymnastics Team of Fairmont, W.Va., where she worked with Olympic gold medalist Mary Lou Retton . . .

The summer plans of Wisconsin safety Robb Johnston were changed by a surgical error that has him hobbling on two fiberglass casts and hospital officials a little red-faced.

Johnston underwent surgery June 13 to remove bone chips in his left foot. But when he woke up in the recovery room at the University of Wisconsin Hospital in Madison, he noticed "bandages on my right foot."

"I couldn't believe it. I told the nurses that they did the wrong foot and at first they didn't believe me," said Johnston, expected to start this season. "They told the doctor (William Clancy), who had treated me during football season for my left ankle. I went back into the operating room and had surgery on my left foot."

Clancy, the team physician, said someone inadvertently marked down the wrong foot and X-rays showed an excess bone growth on the right heel as well as the left. "I've been operating for 14 years and never had a screwup like this," Clancy said.