Two top executives of the Joseph R. Harris Co., a 27-store women's apparel chain owned by Garfinckel, Brooks Brothers, Miller & Rhoads Inc., have resigned their positions with the firm.

President Donald B. Harris, 47, said he wants to pursue "personal interests outside the retail industry" while vice president and general"while vice president and general merchandise manager J. Robert Harris 111 said he plans to start his own business.

No successors have been apppointed and both men will remain in their posts until a new chief executive officer is named, according to the Garfinckel corporation. Informed sources sai Harris employees were told of the resignations, which came as a surprise, last Monday. A Garfinckel spokesman said the departures of the two Harris family members were not based on policy differences or management disputes.

The Harris chain was purchased from the Harris family by Garfinckel in 1971 and the division's chairman, J. Robert Harris Jr., will continue in his post and remain on the Garfinckel board, although he is not active in day-to-day management.

Donald Harris, the outgoing president, said yesterday that he had been with the company since he was 15 years old and , "I have a desire to do some other things...I don't have any thing to announce at this time."

The National Economists Club has elected Courtenay M. Slater president for the coming year. Slater, former vice president of the club, is a senior economist on the staff of the Joint Economic Committee. She has been on the committee's staff since 1969. Prior to that, she was senior staff economist at the Council of Economic Advisers.

The club also elected Joel S. Popkin and Harry S. Schwartz as vice presidents. Popkin is director of the Washington office of the National Bureau of Economic Research, where he is directing inflation studies.Schwartz is vice president and chief economist of the Federal National Mortgage Association and was previously adviser and director of research of the Federal Home Loan Bank Board.

DIRECTORS: Southern Railway Co. has elected John Lucian Smith Jr., president of the Coca-Cola. in Atlanta, to the board.

Booz-Allen & Hamilton, Inc. has elected R. Michael McCullough a director. He is president of the firm's applied research division in Bethesda.

Russell R. Jones of Bethlehem Steel Corp. is a new director of First Maryland Bancorp and its principal subsidiary, First National Bank of Maryland.

Security National has elected Albert C. Borghi, president of Stanford Paper Co., a director.

Maryland Federal Savings and Loan Association has named Mildred Harkness to the board. Harkness is a membe of the Hyattsville city council.

American Finance System, Inc. has elected its executive vice president and chief financial officer, John J. Krieger, a director.

Two new directors of District of Columbia National Bank are Joseph R. Schuble, executive vice president of Dreyfuss Brothers, Inc. and Stanley R.Zupnik, president of Polinger & Zupnik Builders Corp. and Majestic Building Corp.

First & Merchants Corp. has elected retired Admiral Ralph W. Cousins to its board.

Alexandria National Bank of Northern Virginia has elected Joseph M. Guiffre to the board. He is president of the Tony Guiffre Distributing Co. of Alexandria.

Three new directors of Bank of Virginia-Potomac are C. Lacy Compton Jr., Charles W. Rector and Stanley Westreich.

Industrial Training Corp in Rockville has elected John D. Sanders, vice president of Wachtel & Co., Inc., to the board.

Hobart Taylor Jr. of the Washington law firm of Dawson, Riddell, Taylor, Davis and Holroyd has been nominated for election to the board of Eastern Airlines.

Former Navy Secretary J. William Middendorf 11 is the chief representative of a new group of investors seeking to buy 1.2 million shares of Financial General Bankshares, Inc., from International Bank of Washington.

IB, a diversified financial services company, said Friday that Middendorf's group has been given a deadline of 5 p.m., March 18, to consummate such a transaction.