Riggs National Bank, the area's largest financial institution, yesterday added Louis Martin, a Howard University assistant vice president and former Democratic Party presidential adviser, to the bank's board of directors. The bank holding company's board of directors also announced a two-for-one stock split.

Martin, who was named to the bank's advisory committee in July, becomes the first black ever to serve on the board of the regionally powerful bank. Martin's appointment comes several years after other large Washington banks began adding blacks to their boards of directors in late-blooming recognition of the city's racial make-up.

Joe L. Allbritton, who gained control of the bank last spring, said the appointment is a harbinger of other changes that will make the bank board more broadly representative of the community.

"I would think when you start naming men like Louis Martin to the board, that says something," Allbritton said yesterday.

The bank board "has always been superb," he said, but he added that he expects it to reflect "broader representation of our community and that sort of thing" in the future.

Martin, who lives in Chevy Chase, served from 1978 to 1981 as a special assistant to former president Jimmy Carter.

He also served as a presidential adviser in the Johnson and Kennedy administrations and was deputy chairman of the Democratic National Committee. He is an assistant vice president for communications at Howard University.

From 1969 to 1978, he served as editorial director and president of a black newspaper chain, Sengstacke Newspapers, which publishes the Chicago Daily Defender, the Pittsburgh Courier and the Michigan Chronicle. He is chairman of Calmar Communications Inc. and serves on the boards of a Chicago bank and a Chicago savings and loan association.

Eight vacancies were created on the Riggs Bank board when several former directors became directors of Riggs' new bank holding company.

Allbritton took over as chairman and chief executive officer of the holding company, Riggs National Corp., and named his Houston banking associate, Thomas W. Wren, as its vice chairman in early August.

The Riggs bank board has looked like a who's who of Washington's old-line business establishment. It includes two women -- Margaret Truman Daniels and Jaqueline C. Duchange. The latter is the daughter and business associate of a former major shareholder in the bank.

In another development yesterday, Riggs National Corp.'s directors approved a two-for-one stock split for the corporation and fixed the dividend on the split shares at $1.50.

The stock split is subject to regulatory approvals. The board also declared a regular quarterly dividend of 70 cents a share on its outstanding common stock payable Oct. 15 to shareholders as of Sept. 30.