Edward McKenna, 49, who had a general law practice in Washington, died of lung cancer Friday at his home in Falls Church.

He opened his own offices about two years ago and was active until he became ill last June. Before that he was associated with the law offices of Richard J. Leighton and was a lawyer with the Agriculture Department.

Mr. McKenna was born in Astoria, Long Island, N.Y., and earned a degree in physics from the City College of New York.

He came to Washington in 1960 to work as a physicist at the Harry Diamond Laboratories. He also attended the Washington College of Law at American University at night, and earned a degree there in 1970.

Mr. McKenna served in the Army during the Korean conflict. He was a member of the Irish-American Cultural Institute and the Banshees.

He is survived by his wife, Theresa, and three children, Geoffrey L., Anne Diedre and David E., all of the home, and two brothers, Patrick, of Uniondale, Long Island, N.Y., and John Raymond, of Astoria.

The family suggests that expressions of sympathy may be in the form of contributions to the Vienna Chapter of the American Cancer Society.