Jerry Thomas, 51, undersecretary of the Treasury in the last year of the Ford administation and a prominent banker and Republican in Florida, died of cancer Tuesday at his home in Jupiter, Fla.

Mr. Thomas was undersecretary from April 1976, until January 1977. During the 1976 Republican primaries, he headed the Florida Conservative Union and gave its support to Gerald Ford. This was regarded as a setback for Ronald Reagan, who lost the GOP presidential nomination to Ford that year.

A native of West Palm Beach, Mr. Thomas was a graduate of Florida State University. He served in the Marine Corps from 1952 to 1954, and then earned a master's degree in education at Florida Atlantic University in Boca Raton.

He became a stockbroker, and in 1964 founded First Marine Bank, Inc., now a Florida-based bank holding company.He was its chairman and chief executive at the time of his death.

Mr. Thomas became active in Republican politics early in his career. He was elected to the Florida House of Representatives in 1960. From 1964 to 1972, he was a member of the state Senate and was its president from 1970 to 1972. In 1974, he was the GOP gubernatorial candidate against Democrat Reuben Askew, who became the governor.

Mr. Thomas' survivors include his wife, Imogene (Jeannie), two daughters, Robin Bullard and Cindy Thomas, three sons, Jerry, Larry and Kenneth, and five grandchildren, all of Jupiter.