Lynn Swann, the athletic director at the University of Southern California since 2016, abruptly resigned on Monday amid turbulence in the football program, two F.B.I. investigations targeting the athletic department and questions about whether Swann’s connections to the school’s biggest donor had landed him the job, for which he had no previous experience.

Swann’s resignation was announced by the new university president, Carol L. Folt, who said that while U.S.C. conducts a nationwide search for a replacement, the job would be filled on an interim basis by Dave Roberts, a university administrator who is also the vice chairman of the N.C.A.A.’s committee on infractions.

Swann, 67, who was a star receiver for U.S.C. and the Pittsburgh Steelers, had a rocky three-year tenure as the athletic director that included the decision to give the football coach Clay Helton a lengthy contract extension before last season, which ended with a 5-7 record, and concerns about Swann’s responsibility in the scandals that led to the federal investigations. A former assistant basketball coach, Tony Bland, pleaded guilty in a federal bribery case, and four people associated with U.S.C. athletics have been implicated in the nationwide college admissions scandal, a scheme that began in 2014 but continued under Swann’s watch.

The Los Angeles Times last week published an article raising questions about whether Swann — whose résumé beyond his playing career was built largely on his work as a college football television analyst and an unsuccessful run for governor of Pennsylvania — had been hired by the previous university president, C.L. Max Nikias, because of his close relationship with U.S.C.’s biggest donor.