American Security Corp. has named Gerard M. Keeley executive vice president with responsibility for resolving its problem loans, which resulted in a loss for the bank last quarter. Keeley is credited with correcting the loan problems of his former employer, First Pennsylvania Bank, according to an American Security spokesman. Earlier, he served for 24 years with Continental Illinois National Bank and Trust Co. of Chicago, where he rose to senior vice president for general banking services. In his new position, Keeley will report to Daniel J. Callahan III, chairman and chief executive officer.

Joel Fernebok, president of Harvey Construction Co., has been elected to the board of directors of the National Bank of Commerce. Formerly a director of both Security National Bank and Washington Bank, Fernebok will also serve on the bank's loan committee.

First Federal Savings & Loan Association of Northern Virginia has appointed L. Brian Mullen, formerly chief executive officer of Developers Mortgage Corp. of Bethesda, as president and chief executive officer of the Alexandria financial institution. Mullen succeeds Richard F. Downham, who was president of First Federal for 22 years.

Vincent N. Cook, president of International Business Machines' federal systems division and an IBM corporate vice president, was elected a director of Suburban Bank in Bethesda.

Attorney Michael R. Kain and Robert L. Tull, chairman and chief executive officer of the Security Storage Co., have been elected to the board of directors of Washington Federal Savings & Loan Association.

Directors of the National Capital Bank of Washington have elected James H. Thompson Jr., vice president and chief administrative officer, and George A. Didden III, senior vice president, to its board.

Stephen H. Detwiler, a local banking veteran and former president of the Metropolitan Council of Governments, has been named president and chief executive officer of the newly established Acacia Federal Savings Bank in Annandale. Detwiler, formerly with Continental Federal Savings & Loan, also was chairman of the Arlington County Board of Supervisors in 1981 and 1982.