John Debelius, 58, a Montgomery County lawyer and a former security officer with the Central Intelligence Agency, died Nov. 20 at Prince George's General Hospital after a heart attack.

Mr. Debelius had practiced law in Montgomery County since leaving the CIA in 1971. He had been with the agency since 1954, when he settled in this area, and before that had been a special agent with the FBI for five years.

A resident of Gaithersburg, Mr. Debelius was born and reared in Baltimore and served two years in the Army at the end of World War II. He was a graduate of Georgetown University's School of Foreign Service and the University of Baltimore law school.

He was a member of St. Mary's Catholic Church in Barnesville.

Mr. Debelius' first wife, Mary, died in 1981.

He is survived by his wife Elizabeth, of Gaithersburg; three daughters by his first marriage, Anne Debelius of Adelphi, Peggy McKelly of Los Angeles, and Air Force Capt. Elizabeth Debelius of Marquette, Mich.; two sons by his first marriage, John W. and James J., both of Gaithersburg; two brothers, Chuck, of Alexandria, and Harold, of Madrid; a sister, Kay Robertson of Virginia Beach; a stepson, Attila Toth of Fairfax, and one granddaughter.