Two Virginia horse country estates were recently acquired by corporations controlled by sports executive Jack Kent Cooke, who earlier purchased an 18-room stone house on 50 acres near Upperville, Va.

Cooke, who owns principal interests in the Washington Redskins, the Los Angeles Lakers and The Forum sports arena in Los Angeles, is the man behind the Raljob Corp., which recently took title to the 360-acre Byrnely Farm, near The Plains, Va., where Cooke's son now lives.

Byrnely was formerly owned by Athalie R. Clarke, who is the mother of Joan Irvine Smith, holder of a principal interest in the vast Irvine ranch development in Orange County, Calif.

A realty broker said the Byrnely transaction was actually an exchange of the $2 million property for Cooke properties in California.

In another recent transaction involving Cooke, Samuel A. Furcron, along with his wife and others, deeded the 211-acre farm known as The Glebe on Rte. 55, near The Plains, to the Forum of Inglewood (Calif.) Inc. This adjoins the Byrnely farm. The Fauquier County property was acquired for what was reported as a consideration of $595,000 but actually was a property trade with the seller getting stock in The Forum of Inglewood (Calif.) in exchange for the acreage.

A house on five acres of the original farm known as The Glebe is still owned by Kay Calvert of Washington.