Charles Joseph Harnett, 74, a Northern Virginia businessman and civic leader for many years, died Friday at Arlington Hospital. He had suffered from a heart ailment.

At the time of his death, he was secretary-treasurer of Clarence W. Gosnell Inc., a building firm that he had joined in 1930. He formerly had served as its vice president.

Mr. Harnett also had been an officer for many years of the Monroe Development Corp., a real estate firm. Until recently, he was a director of the First Viginia Bank in Fairfax County and a member of the board of trustees of Fairfax Hospital.

Born in Rye, N.Y., Mr. Harnett attended Union College in Schenectady. He came here in the mid-1920s to attend Georgetown University Law School, and graduated in 1929. He started in the real estate business while in school.

During World War II, he served as a combat intelligence officer with the Army Air Forces in the Caribbean and South America.

Mr. Harnett was a past president of the Home Builders Association of Metropolitan Washington and the Northern Virginia Builders Associations. He had been a director of the National Association of Home Builders, the Surburban Virginia Home Builders and the Home Builders of the State of Virginia.

He was a past president of the Fairfax Chamber of Commerce and the Mount Vernon - Lee Chamber of Commerce. He was a former vice president of the Hospital Council of Metropolitan Washington and a former director of the Northern Virginia Heart Association.

Harnett was a member of the D.C. and Virginia bars and was admitted to practice before the U.S. Supreme Court. He belonged to the D.C. Arlington and Virginia bar associations.

He is survived by his wife, Helen F., of the home in Arlington; a daughter, Joan H. Hathaway, of Augusta, Maine, and four grandchildren.

The family suggests that expressions of sympathy may be in form of contributions to the Northern Virginia Heart Association.