George W. Allen Sr., 74, founder and operator of his own real estate company in Montgomery County and a former president of the Montgomery County Board of Realtors Inc., died of cancer Saturday at Holy Cross Hospital in Silver Spring.

Mr. Allen was born in Cincinnati and grew up there, in Washington and in Denver. He served in the Coast Guard in the early 1920s and moved to the Washington area permanently in 1927.

He was a streetcar operator for the old Capital Transit Co., a fore-runner of Metro, and during World War II instructed women bus drivers and trolley car operators for the system. He also gave instruction in first aid.

In 1952, he left Capital Transit and went into the real estate business. Two years later, he founded his own firm in Washington. It is the George W. Allen Real Estate Co. and has been located in Wheaton for several years. While running his own business, Mr. Allen also served as a real estate appraiser for the Veterans Administration and other government agencies.He remained active in his own company until his death.

Mr. Allen, who lived in Silver Spring, also remained active in the Montgomery County Board of Realtors Inc. he was a director of the organization at his death and had been its president in 1969. In 1979, the board named him "Realtor of the Year."

Mr. Allen was a member of the First Baptist Church in Wheaton and had served it in numerous capacities, including that of trustee.

Survivors include his wife of 56 years, Alma, of Silver Spring; three sons, George W. Jr. of San Jose, Calif., Millard of Winchester, Va., and Robert of Silver Spring; four grandchildren, and one great-granddaughter.

The family suggests that expressions of sympathy be in the form of contributions in Mr. Allen's memory to the First Baptist Church in Wheaton.