Diagnon Corp., a publicly held biotech firm in Laurel, has named Dr. John C. Landon as its president and chief executive officer and purchased his Rockville company, Bioqual Inc., for an undisclosed amount.

Landon, who has been affiliated with Diagnon as co-owner of its SEMA Inc. subsidiary since last year, was filling in as general manager of the company before his appointment two weeks ago. Landon and directors of Diagnon had mentioned a possible partnership between the companies for "about two years."

"In the past, there has been a lot of talk; now there's action. Bioqual folded into Diagnon and the three companies Diagnon Corp., SEMA Inc. and Bioqual Inc. will come under my management as president. The management will change with company growth, but for now that's how it will operate," Landon said.

As president, he replaced Dr. William C. Gordon, who was holding the position temporarily. Gordon returned to his post as vice president of research development at Diagnon.

Landon, a noted biotechnologist who has researched cancer and infectious diseases for 25 years, opened Bioqual in 1982. The company conducts research in immunology, transgenetics (research on gene transfers), allophenic development (the breeding of new kinds of animals to be used in cancer studies) and congenic animal breeding (research on inbred animal strains) and is under contract to the National Institutes of Health. The company will continue its research under its parent company.

Prior to that, Landon was president and director of EG & G Mason Research Institute, which has facilities in Rockville and Worcester, Mass., where he was responsible for a 275-person research staff.

Diagnon, which was founded in 1981 to research and develop diagnostic tests for infectious diseases, teamed up with Landon for the first time in 1985. The partnership formed SEMA Inc., which soon acquired five Meloy Laboratories contracts. The contracts, to conduct research and vaccine development for NIH, bring the company approximately $100,000 a year, Landon said.

Under the new management, Landon said, each company will retain separate functions. SEMA and Bioqual will continue conducting research under contracts with NIH. Diagnon, still in its "developmental stage," eventually will market its diagnostic tests through distributors.

"The government contract work is very similiar between Bioqual and SEMA, so there is a certain fit," Landon said. "The commercial aspect of Diagnon is very different, but eventually the companies will help each other. Certainly, for me, it will be much easier to manage the companies as one organization." BANKING, FINANCIAL SERVICES

The Federal Home Loan Mortgage Corp. appointed Anthony J. Sulvetta vice president of corporate finance, in which capacity he will oversee the management of the company's investing and finance activities. Prior to his appointment, he headed the investment research firm Justin Research Associates. In 1983 and 1984, Sulvetta served as deputy assistant secretary and chief economist for the U.S. Department of Housing and Urban Development. The company also appointed 22 new members to its 1986 advisory committee. The 45-member board counsels the management and board of directors on long-range trends in housing finance.

The National Bank of Commerce named Frederick E. Rigney senior vice president and chief administrative officer. Rigney, who joined the bank in July, is a 14-year veteran of the industry. The bank also promoted Diana Chimes to vice president and controller and H. M. Lee DeWitt to vice president of commercial lending.

First Women's Bank of Maryland promoted Robert M. Haynes from vice president of operations to senior vice president and cashier. Haynes joined FWB in May 1985 from Chevy Chase Savings & Loan, where he was director.

William M. Lucianovic, formerly with Coopers & Lybrand, joined the Washington CPA firm KMG Main Hurdman as director of the national management consulting services group.

ICA Mortgage Corp. named Richard J. Nenna regional vice president of its Greenbelt office. In his new position, he will be responsible for setting up two branch offices and a regional headquarters in the metropolitan area. Nenna previously worked for Citizens Mortgage of St. Petersburg, Fla., where he was also regional vice president. COMMUNICATIONS

Public Broadcasting Service announced two promotions: Eric Sass to senior vice president of administration and computer services and Alfred A. Norcott Jr. to director of interconnection facilities. Sass, who joined PBS in 1978, previously served as vice president of administration. Norcott, who joined the company in 1985, will oversee the construction of PBS' technical center and the operation of the satellite facilities.

Naomi P. Salus, formerly with the Federal Reserve System as special assistant to the Board of Governors, left her position to open the financial public relations firm NPS Associates Inc.

Pamela Johnson, former executive director of the Museums Collaborative in New York, joined the public relations firm Rogers & Cowan Inc. as vice president of corporate cultural affairs. Johnson replaced Elizabeth A. C. Weil, who joined the National Gallery of Art as corporate relations officer. GOVERNMENT

William R. Hunt was named director of Navy laboratories, succeeding Gary W. Morton, who left the position to become the science and technology adviser at the Naval War College in Newport, R.I. Hunt worked for the Naval Air System Command for 20 years and most recently served as technical director for research and technology. In his new position, he will oversee an operating budget of $2.5 billion, a staff of 25,000 and four university laboratories that conduct applied research and development for the Navy.

Collister Johnson, senior vice president of Presidential Airways, will replace Robert H. Spilman as chairman of the board of commissioners of the Virginia Port Authority. Johnson has served on the board since 1982. W. Wright Harrison, former Sovran Bank chairman of the board, was named board vice chairman. INDUSTRIAL, MANUFACTURING

Hekimian Laboratories Inc., a manufacturer of microprocessor-based telecommunications equipment in Gaithersburg, promoted Lawrence E. Keith to vice president of marketing. Keith joined the company last year. NONPROFIT

Donald Elisburg, a partner in the law firm Connerton, Bernstein and Katz, was named administrator of the legal defense fund Occupational Health Legal Rights Foundation. Elisburg was assistant secretary of labor in charge of the employment standards administration from 1977 to 1981.

Michael S. Clark, a management and fund-raising consultant, was selected from 200 applicants to head the lobbying group the Environmental Policy Institute as president. Clark will replace Brent Blackwelder, who had served as acting president since January.