Now that Harry F. Byrd Jr. has left the U.S. Senate, concluding nearly 50 years of father-and-son service, the University of Virginia finds itself with a remarkable abundance of Harry F. Byrd Jr. professorships.

Not one, but two, professorial seats named for the scion of the Virginia political family have been established at Charlottesville, both from benefactions from the estate of James F. Lewis Jr. Lewis was a Champion Spark Plug Co. executive and resident of Albemarle County, of which Charlottesville is the seat.

One Byrd professorship is in government and foreign affairs, fields in which the senator left an imprint. The other is in biochemistry.

Two other endowed professorships have been created, one in rheumatology named for the late Margaret M. Trolinger, who bequeathed the funds, and the other in business, with funds contributed largely by Arthur Andersen & Co. and that accounting firm's employes.

The endowed professorships bring to 50 the number established at U-Va. since the beginning of the school's three-year capital fund drive, which has a goal of $90 million.

The university's Board of Overseers also named Peter Taylor, a short story writer, as professor emeritus. As the Henry Hoyns professor of creative writing, he retired at the end of this school year after serving on the faculty since 1967.

Other retirements: Dr. C. Cabell Bailey, clinical professor of medicine; Robert T. Barbee, associate professor of studio art, and George H. Reese, professor of humanistic sources.