Bernard Saunders Van Rensselaer, 91, who formerly worked in U.S. foreign aid programs and then became director of the senior citizens division of the Republican National Committee, died of cancer Wednesday at his home in Washington.

A native of New York, Mr. Van Rensselaer was educated at Harvard College. Cornell Law School and the University of Pennsylvania Law School. He began his government career in 1942, when he served with several World War II economic agencies, He previously had practiced international law and banking in New York and South America.

After World War II, Mr. Van Rensselaer was a branch chief in Southeast Asia for the Mutual Security Administration. Later, he conducted an investigation of military and economic foreign aid for the Senate Appropriations Committee headed by the late Sen. Styles Bridges (R-N.H.). He retired in 1955.

Hr then became interested in the problems of the elderly. He served as director of the senior citizen division of the Republican National Committee from 1959 to 1974. He became known as "Mr. Senior Citizen" as a result of his travels throughout the United States on behalf of legislation affecting older americans.

Mr. Van Rensselaer also was a vice chairman of the Mayor's Committee on Housing for the Elderly and a member of the Interfaith Task Force on Senior Citizens in the District of Columbia.

He was a member of Christ Eposcopal Church and the visiting committee of the Washington Home for Incurables. In addition, he was a past president of the New York State Society of the Cincinnati and member of the Sons of the Revolution. The Harvard Club of Washington and the Capitol Hill Club.

Survivors include his wife, Charlotte Mary and a son, Henry C., both of the home in Washington; a brother, Kiliaen M. of Alburqueque, N.M.: a sister, Maud, of Hintington, N.Y., and two children.