Robert H. Zalokar will become chairman and chief executive officer of First Virginia Banks Inc. following the retirement Dec. 31 of Thomas K. Malone Jr., the bank holding company's chief executive for the last six years. Paul H. Geithner Jr. will succeed Zalokar as president and chief administrative officer.

Malone, 65, has been a fixture at the Falls Church-based holding company since 1948 when he joined First Virginia's predecessor, Old Dominion Bank, as a part-time teller. Fourteen years later, he was named president of Old Dominion.

In 1969, Old Dominion merged with Falls Church Bank and Mount Vernon Bank and Trust Co. to form First Virginia Banks Inc. Malone remained with the new company and in 1976 was recruited to help its financially troubled real estate subsidiary, First Virginia Mortgage and Real Estate Investment Trust. Under Malone's leadership, First Virginia has acquired 13 banks, doubled its assets and tripled its earnings.

First Virginia operates primarily in the Northern Virginia area. It has assets of $2.6 billion, making it the sixth largest bank in Virginia.

Zalokar is a 57-year-old native of West Mineral, Kan. He began his career as a bank examiner in the Washington area for the Federal Deposit Insurance Corp. Zalokar was appointed president of Old Dominion Bank in 1965 after 10 years with the bank, and was elected president of First Virginia Banks Inc. in 1979.

Zalokar has held positions in several banking industry groups. He was a member of the governing council of the American Bankers Association, Virginia vice president of the ABA and chairman of the federal legislative committee of the Virginia Bankers Association.

Besides being chosen First Virginia's new president, Geithner, 54, has been elected a director of the corporation. He joined First Virginia in 1968 after working for Ellicott Machine Corp. in Baltimore as secretary and treasurer. Geithner was elected senior vice president of First Virginia in 1975, and most recently served as senior vice president and executive assistant to the chairman and president.