Emmett J. Rice, senior vice president of the National Bank of Washington, has emerged as a leading contender for one of two vacancies on the powerful Federal Reserve Board.

President Carter, it was learned, directed that one of the two posts go to a balck, in delegating to Vice President Walter F. Mondale the job of proposing names of prospective Fed governors.

In keeping with his desire to assure a greater diversification of talent on the board and representation of minorities, Carter last year appointed the first woman to the Fed, Nancy Teeters, to fill the vacancy left when Arthur F. Burns resigned as a governor.

Rice would meet Carter's desire for a black governor -- the first since Andrew F. Brimmer resigned in 1974 -- and Federal Reserve Chairman G. William Miller's wish to have a commercial or mortgage banker among the members.

Although trained as an economist, with early experience on the staff of the New York Federal Reserve Bank, Rice since 1971 has been in charge of the National Bank of Washington's money center operations, or all of the bank's commercial activity.

But White House sources, although they expect an announcement of at least one appointment shortly, stressed over the weekend that the President had made no firm decisions.

Miller said recently that the seven-member Federal Reserve Board must get away from a tendency to concentrate on economists and seek talents in the business, banking, housing, agriculture or labor fields.

The two vacancies were created by the resignation of Philip Jackson, a housing specialist whose term had until Jan. 31, 1982 to run; and the death of former banker Stephen S. Gardner, whose term would have run until Jan. 31, 1990.

Rice is a Democrat and considered to be middle-of-the-road in his approach to economic policy.

Two other blacks whose names have been mentioned in public speculation for the Federal Reserve job are Bernard Anderson, associate professor of economics at the Wharton School of the University of Pennsylvania, and James Tucker, a vice president of the Richmond Federal Reserve Bank.

President Carter also is actively seeking a minority representative to succeed William Nordhaus, who is leaving as one of the three members of the Council of Economic Advisors. There has been neither a black nor a woman on the CEA since its inception in 1946.

Others who are possible appointees to the Federal Reserve include Luther Hodges Jr. of North Carolina, who ran an unsuccessful race for political office last fall; Michael Sumichrast, chief economist of the National Association of Home Builders; and Lyle Gramley, a current member of the economic council.

Rice was born in Florence, S.C., and received a bachelor's degree from the City College of New York in 1942. After serving in the Air Force, Rice was a fireman in Berkeley, Calif., before studying for his Ph.D. at the University of California, which he received in 1955.

He taught briefly at Berkeley, then at Cornell University, before joining the Fed staff in New York in 1960. From 1960 to 1964 Rice helped establish the Central Bank of Nigeria, when that country gained its independence.

After two years at the U.S. Treasury as a deputy director in the international affairs department, Rice was appointed by President Johnson in 1966 as an alternate executive director for the U.S. at the World Bank.