At Geico Corp., the changing of the guard -- begun with the departure last July of the insurance company's dynamic leader, John J. Byrne -- continues.

Last week, the insurance monolith named Eugene J. Meyung, an eight-year veteran of the company, to the position of president of the Government Employes Insurance Co., an automotive and homeowners insurance company that is Geico's largest subsidiary.

The appointment completes the succession begun last year when Byrne became chairman and chief executive officer of Fireman's Fund Corp., the insurance subsidiary of American Express Co.

Meyung, 60, succeeds William B. Snyder in the post of president. Snyder, who will continue as chairman and chief executive officer of the subsidiary, replaced Byrne in the company's top slot last year.

"Gene's successful performance . . . has proven that he knows what must be done to achieve profitability and productivity and, more importantly, how to do it," Snyder said.

In an interview, Meyung said the recent changing of the guard would not affect the management of Geico or its subsidiary.

"Geico is a two-note company. We concentrate on auto and homeowners insurance. Years ago, we set the company disciplines, and people moving through the chairs don't have that much effect as long as we stick to our discipline," Meyung said.

Of the two new business prospects mentioned at the time of Byrne's departure, Meyung said that one -- Geico's potential acquisition of the property-casualty insurance business of Fireman's -- is no longer being seriously considered by the two companies. The other -- allowing Geico to market its automobile insurance policies to American Express cardholders -- is still a possibility, Meyung said.

Meyung, a native of Virginia and a 25-year veteran of State Farm Insurance Co., said that his responsibilities for running the day-to-day business of the subsidiary that accounts for about 85 percent of Geico's revenue "won't change all that much." He will remain in charge of operations, including the servicing and handling of claims and pricing.

Meyung, a graduate of the University of Virginia law school, joined GEICO in 1978, where he served as a regional vice president and senior vice president before being named executive vice president in 1981. Meyung will retain his former duties, he said, and no successor will be named.

On Friday, Meyung attended all-day meetings reviewing the performance of GEICO in 1985 with the heads of each of the company's six profit centers. Meyung said he was disappointed that the company did not meet its goals for achieving a gain in the underwriting business, even though GEICO fared well compared with "our brothers in the industry." But, he said, "We don't take any pride in being the least of a group of losers." PROFESSIONAL SERVICES

The MITRE Corp., a government contractor based in Boston, has promoted John S. Quilty to vice president and co-manager of the firm's McLean division. He was formerly technical director of national command and control systems.

Verdix Corp., a computer systems and software development company, has named Albert N. Wergley director of legal services for the Chantilly firm. He was previously with the McLean law firm of Reed, Smith, Shaw & McClay.

Melvin S. Day, a veteran government administrator who was formerly director of the National Technical Information Service, has been named senior vice president of the Arlington firm of Herner & Co., which plans, operates and services libraries and information systems.

URS Corp., a diversified technical services firm, has recruited Kenneth S. Kamlet as environmental program director of its environmental services group. Kamlet had been director of the National Wildlife Federation's pollution and toxic substances division.

AMAF Industries Inc., a Columbia systems engineering and high-tech services firm, has named as its president William A. McConarty, an engineer who was previously executive vice president. He will continue to serve as treasurer of the firm.

Nancy J. O'Brien, former business manager of The Aaron Group, has been promoted to director of business administration for the trade show and exposition contracting firm, which is based in Alexandria.

ORI Inc., a Rockville professional and technical services firm, has promoted Art R. Milkes to corporate executive vice president. Milkes sits on the board and is chief financial officer for the three ORI companies -- ORI Inc., CALCULON Corp. and Intercon Systems Corp. David L. Reed, who heads ORI Inc.'s aerospace systems group, has been named senior vice president for the company.

The Washington architectural firm of Keyes Condon Florance has named three new associates: Steven Kleinrock and David Ricks, who have served as project architects, and North Sturtevant, who is director of construction administration.

Lewis/Wisnewksi & Associates Ltd. has appointed Susan L. Norton, former communication manager for Greenhorne & O'Mara Inc., to the post of marketing manger of the Alexandria architectural firm.

Tom Lewis Peyton Jr., formerly director of facilities services for the Smithsonian Institution, has been named to the post of assistant to the president of Leo A. Daly, an international architectural firm.

Iverson Technology Corp. in McLean has appointed Joseph D. Zanin vice president for development and quality assurance of its TEMPEST computer security products. Zanin, a specialist in communications security, had been with the Central Intelligence Agency for 22 years. COMMUNICATIONS

Doremus & Co., which is based in New York, has appointed Daniel S. Buser Jr. vice president and general manager of the advertising and public relations firm's Washington office. He was director of public relations at the American Bankers Association for the past eight years.

The Communications Satellite Corp. has elected Marcel P. Joseph to its board of directors. Joseph became president and chief operating officer of the congressionally chartered company in October.

Earle Palmer Brown Cos. in Bethesda has named Ronald R. Mueller to the new post of president of its public relations division. Mueller, who joined the firm in 1984 as vice president and general manager, assumes overall responsibility for the firm's three offices.

Edward H. Moore, formerly vice president and assistant general manager, has succeeded Mueller as general manager of the agency's Bethesda headquarters. In a separate announcement, Roy B. Pinchot, a former vice president of a Chicago printing paper distributing company, has been tapped as vice president and account supervisor of Brown Direct, the direct marketing division of Earl Palmer Brown. INDUSTRIAL, MANUFACTURING

Reuter Laboratories Inc., a manufacturer of biological pesticides in Manassas Park, has promoted Carter H. Marantette to the post of president. He was formerly divisional sales manager for the western and southeast markets.

The Ryland Group Inc., a Columbia firm that builds and sells residential housing, has promoted John F. Canning to senior vice president and president of the company's mid-Atlantic area.

Richard N. Vaswani, an accountant who joined OMNI Construction Inc. a year ago, has been named corporate treasurer and chief financial officer of the Bethesda construction firm. BANKING, FINANCIAL SERVICES

Randall S. Jenkins, an investment banker, has formed a firm specializing in managing private security offerings for limited partnerships, Placement Management Services Inc., which is located in Gaithersburg.