John Lloyd Catalan, 59, assistant general counsel for finance at the Energy Research and Development Administration, died of a respiratory ailment Saturday at Georgetown University Hospital.

Mr. Catlan served for 12 years as an attorney with the Atomic Energy Commission before being appointed as ERDA's assistant general counsel for finance in 1975.

Born in Nashville, Tenn., Mr. Catlan grew up in Louisville, Ky., and Cleveland, Ohio. He attended Wilberforce University in Ohio from 1936 to 1938.

After serving with the U.S. Army in the South Pacific in World War II, he became a student at Long Island University and later received his bachelor's and master's of law degrees from Brookland Law School.

From 1950 until 1957, Mr. Catalan was in private practice in New York City and Brooklyn, specializing in workmen's compensation and negligence claims.

He then became a senior property attorney with New York State Department of Law, based first in Albany and then in Rochester, before joining the AEC.

Mr. Catalan was a life member of the NAACP and a member of the Federal Bar Association. He was admitted to practice before the Appeals Courts of New York and of Maryland and was a member of the bar of the U.S. Supreme Court.

He had been a member of the Montgomery County Commission on Human Relations and was a former chairman of the Montgomery County Commission on Landlord and Tenant Affairs.

He is survived by his wife, Shirley Catalan, of the home in Silver Spring; his mother, Irene Catalan Yates, of New Haven, Conn., and a sister, Muriel Catalan Crowley, of Hamden, Conn.