William P. Gwinn, 74, who rose from stock clerk to chief executive of the United Aircraft Corp., now United Technologies Corp. of Hartford, Conn., during his 45-year career in aviation, died of cancer Friday at Good Samaritan Hospital in Palm Beach, Fla.

Mr. Gwinn headed the corporation's largest unit, Pratt & Whitney Aircraft, for 14 years, directing the firm's massive World War II engine production and its postwar transition from piston to jet propulsion. Pratt & Whitney, which shipped more than 363,000 aircraft engines during the war, now is the world's largest producer of jet engines for commercial and military aircraft.

Mr. Gwinn was responsible for Pratt & Whitney's special efforts to meet the demands of the 1948 Berlin Airlift. He also directed expansion of the firm's production facilities during the Korean war.

He was elected president and chief administrative officer of United Aircraft in 1956 and became the corporation's chief executive in 1968. He also was a member of the board of directors and its executive committee. He retired as chairman and chief executive officer in 1972 and from United's board of directors in 1974.

A native of New York City, Mr. Gwinn attended the Gunnery School in Washington, Conn., before joining Pratt & Whitney Aircraft as a stock clerk at age 19. He spent 10 years in the sales department and opened and managed the firm's West Coast office before becoming general manager in 1942.

He received the Navy Department's Meritorious Public Service Citation and the American Society of Metals' Medal for Advancement of Research. In 1967, he was named Air Cargo Man of the Year by the Air Freight Forwarders Association.

Survivors include his wife, Rachel Coleman Witman Gwinn, of Palm Beach; a daughter, Linda C., of New York City; two sons, W. Clark, of Longwood, Fla., and Michael P., of Alexandria; a sister, Anne Ellison of New York City, and four grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society or a charity of one's choice.