Dr. Andrew W. Breidenbach, 55, a former official of the Environmental Protection Agency and the Maryland State Health Department, died May 23, in a hospital in Paoli, Pa. He had cancer.

Dr. Breidenbach was an authority in the treatment of water wastes. He was chief of the chemistry division of the Maryland State Health Department from 1953 to 1956.

From 1956 to 1975, he worked on waste treatment projects in Cincinnati Ohio, for the Department of Health, Education and Welfare, and then for the EPA.

He came to Washington in 1975 as assistant administrator for water and hazardous materials of the EPA and was promoted to special assistant to the EPA Administrator in 1977.

He retired from government service a year later and was a vice president of the Roy Weston consulting engineering firm in Pennsylvania at the time of his death.

Dr. Breidenbach was born in Newark, N.J. He earned a bachelor's degree in chemistry and zoology at the University of Cincinnati and master's and doctoral degrees in biochemistry at the University of Florida.

At the time of his death, he maintained a home in Bethesda and an apartment in Paoli. His family planned to move to Pennsylvania shortly.

Surviovors include his wife, Jeanne, three sons, Charles, Scott, and David, and a daughter, Barbara, all of Bethesda.