Two great-grandsons of Henry Ford have been elected to the board of directors of Ford Motor Co., an action that appears to ensure the presence of a Ford descendant in the board room for the next several decades.

The new members of the 20-seat board are Edsel B. Ford II, 39, the only son of Henry Ford II, who died of pneumonia in September, and William (Bill) Clay Ford Jr., 30, the only son of company Vice Chairman William Clay Ford.

"As members of the founding family, no one could have more of an interest in the continuing success of the company," said Ford Chairman Donald E. Petersen, who announced the elections yesterday. They were elected at a board meeting Thursday.

Ford has been a public company in January 1956. But the Ford family, holders of a special Class B stock, still control 40 percent of the voting rights. Most people familiar with the company's history and leadership assume that Edsel II and cousin William Jr. eventually will rise to the top of the corporation. But they say that the prospective elevations are not preordained.

Edsel II, in a 1982 interview with The Washington Post, agreed there "are no crowned princes" at Ford.

All officials at Ford go through lengthy periods of testing, Edsel II said, then serving as marketing plans manager for the company's Ford Division. The key to success at Ford is teamwork, he said.

Ford, the nation's second-largest auto maker, was incorporated in 1903 and run as an industrial patriarchy by founder Henry Ford, who retired as its president in 1945, two years before his death April 7, 1947.

The founder's son, Edsel B. Ford, briefly served as president of the company before his death in 1943.

Henry Ford II, grandson of the founder, became company president in 1945 and held that post until 1960, when he became chairman, a position he held until 1980.

Edsel II, a graduate of Babson College, a small but highly regarded business school in Babson Park, Mass., began his career at Ford as a 20-year-old sales trainee. He later served in several district sales office positions; and from 1978 to 1980, he served as assistant managing director of Ford of Australia. He returned to the Ford Division in the United States in 1981, became advertising manager of the division in 1983 and has served as general sales manager of the company's Lincoln-Mercury Division since June 1987.

William Jr. also is considered a "fast-tracker" at Ford. He joined the company in 1979 as a product planning analyst, served in a district sales office and worked with the company's bargaining team in 1982 negotiations with the United Auto Workers union. He later held an advertising position with the Ford Division and then completed a year's study as an Alfred P. Sloan Fellow at the Massachusetts Institute of Technology.

After holding positions in finance and product planning, William Jr. was named director of commercial vehicle marketing for Ford of Europe in 1986. He was elected to his present position as chairman and managing director of Ford of Switzerland in Zurich last September.