DETROIT — Renaldo "Obie" Benson, who for more than 50 years provided the bass vocal foundation to the Four Tops' lush harmonies, died yesterday at Harper University Hospital in Detroit. He had turned 69 June 14.

Mr. Benson had been battling a sudden onset of medical problems.

Last month, he had a heart attack after the amputation of a leg because of circulation problems. He was subsequently diagnosed with lung cancer and began intense, stage-four chemotherapy last week.

Abdul "Duke" Fakir and Levi Stubbs remain the two surviving members of the Four Tops, founded in 1954 on Detroit's northeast side and heralded as one of the longest-running acts in the history of U.S. popular music. Vocalist Lawrence Payton, Mr. Benson's closest boyhood friend, died in 1997.

Mr. Benson "enjoyed every moment of his life," Fakir said through a publicist yesterday. "He put a smile on everyone's face, including my own."

Mr. Benson, who played a key role in directing the Four Tops' concert choreography, was known as a reliable source of comic relief within the group, which was a veteran ensemble by the time it signed on with Motown Records in 1963.

The quartet's statistics on the Billboard pop charts remain formidable: 24 hits in the top 40, seven in the top 10, and two No. 1s.

Many of the songs Mr. Benson recorded with his group remain radio staples, including "Reach Out I'll Be There," "Standing in the Shadows of Love" and "Bernadette."

Mr. Benson rarely slowed down during his tenure with the Tops, who celebrated their 50th anniversary with a bash at the Detroit Opera House last summer.

As he hit his 60s, he continued to spend more than one-third of each year on the road, performing Four Tops shows across the world.

As his condition worsened in recent weeks, Mr. Benson was replaced onstage by Payton's son, Roquel Payton.

Mr. Benson is survived by two daughters and an ex-wife.