William T. Darden, 68, a retired consultant to defense contractors and a former wool merchant, died of cancer Monday at Sibley Memorial Hospital.

From about 1951 until his retirement last year, Mr. Darden ran his own consuilting firm for contractors whose defense, space and other government contracts were subject to review by the old Renegotiation Board.

The board, established in 1951 on a "temporary" basis to recover excessive profits from defense contractors, was terminated in March 1979, when Congress failed to extend it.Mr. Darden retired at that time.

During his consulting career, he wrote a number of manuals on guidelines for contractors dealing with the Renegotiation Board.

Mr. Darden was born in Adel, Ga., and attended the University of Georgia.

He moved to the Washington area in the 1930s to work for the Department of Agriculture and was in charge of purchasing wool for the military during World War II.

After the war, he was a wool merchant in Boston for several years.

A former resident of University Park, he recently moved to Mayo, in Anne Arundel County.

Mr. Darden was a member of Elks Lodge 622 in Annapolis and the Terrapin Club.

Survivors include his wife, Mary Katherine, of Mayo; a daughter, Martha D. Middleton of College Park; a son, William T. Jr., of Asheville, N.C., and two grandchildren.

The family suggests that expressions of sympathy be in the form of contributions in his name to the Memorial Sloan-Kettering Cancer Center in New York City.