Jack F. Davis of Richmond, the former director of the Virginia prison system, is returning to work for his old boss, U.S. Sen. Harry F. Byrd of Virginia.

Until 1974, Davis, 57, was general manager and executive editor of the Byrd-owned newspaper, the Winchester Evening Star. Davis then left the paper after 13 years in Winchester to join the staff of Gov. Mills E. Godwin as a senior executive assistant. He remained in Richmond, serving as director of the often-troubled Virginia corrections department from July 1974 until April 30, 1977.

However, Byrd's office has confirmed that Davis rejoined the senator in Washington this week as his administrative assistant, replacing J. Philip Reberger, 35, of Annandale.

Reberger last year managed Byrd's successful re-election campaign against Democrat Elmo R. Zumwait. An elections specialist, Reberger will leave Byrd's staff in "late August" to become state campaign manager for U.S. Sen. James A. McClure (R-Idaho), who will seek re-election next year.

A native of Idaho, Reberger has long been active in Republican Party politics. He joined Byrd's staff in December, 1973, after serving as a consultant and deputy director for Godwin's successful race for governor as a Republican against Henry E. Howell, who ran as an independent.