Kwasi Holman, the director of the District's Office of Business and Economic Development for the past 4 1/2 years, is resigning to take a top-level post with the National Bank of Washington.

Holman, who also serves as chairman of the influential Redevelopment Land Agency, which controls the city's urban renewal programs, said he will become vice president and manager of small-business banking, a new position at the bank. He said he expects to leave the District government within a few weeks.

The bank maintains several accounts for the District government and is a major financial backer of development projects in the city, according to officials. Holman said he will not be working in those areas.

Small-business banking "is a new area for them," Holman said. He said the bank believes small-business finance is "an emerging area in the region and would like to take the lead."

Holman is the latest of several officials who have said they are leaving or have left Mayor Marion Barry's administration in recent months.

Barry's staff director, Brenda Williams, is scheduled to leave in January. George Thomas, controller of the mayor's office, has requested a transfer to another agency. Melvin W. Jones, former director of finance and revenue, left in August and no permanent replacement has been announced.

Barry also has not filled the position of deputy mayor for finance since March 1986, when Alphonse G. Hill resigned amid allegations of conflicts of interest.

District government sources said yesterday that at the start of Barry's third term in January, Holman had hoped to be named deputy mayor for economic development, a post that went to Carol B. Thompson. The sources said, however, that Holman's decision to leave was based primarily on the appeal of the banking job rather than any disappointment over the deputy mayor's post.

Holman said yesterday that he agreed in January to remain in the District government one more year: "I committed to stay another year with the mayor's team and I did." He declined to reveal his new salary but city officials said they believed it is substantially above his government salary of about $70,000.

In a statement released yesterday by the mayor's press secretary, Barry praised Holman as someone who has been "an important part of this government." The statement said that "some of the best and the brightest work in the Barry administration" and that "private industry is always interested in this type of individual."

Holman, a native of Atlanta, is a graduate of Wesleyan University and holds a law degree from Howard University. He formerly worked for the federal Consumer Product Safety Commission and was an executive assistant in the District city administrator's office.