Norfolk Southern Corp. yesterday named Arnold B. McKinnon, the railroad company's executive vice president for marketing, to succeed Robert B. Claytor as chairman and chief executive.

McKinnon, 58, will join the board of directors and become vice chairman July 1, and will take on the top titles when Claytor, 64, retires Dec. 31.

McKinnon joined the Southern Railway System in 1951, the same year Claytor joined the Norfolk and Western Railway. The two railroads were merged in 1982 to form Norfolk Southern, now a diversified transportation company based in Norfolk. It reported 1985 profits of $500.2 million on revenue of $3.8 billion.

McKinnon started in the legal department of Southern Railway and became executive vice president for law and finance a year before the merger. A native of Lumberton, N.C., McKinnon holds bachelor's and law degrees from Duke University and is a director of the American Security Corp., parent company of American Security Bank.

Claytor has served as chairman and chief executive of Norfolk Southern since it was formed, and was president and chief executive of Norfolk and Western at the time of the merger. He is a graduate of Princeton University and Harvard Law School.

Some observers had expected Norfolk Southern's President Harold H. Hall to succeed Claytor.