Edwin W. Mueller, 65, a physicist who invented the field ion microscope that allowed him to be the first person to see an atom, died Tuesday at George Washington University Hospital.

An Evan Pugh professor emeritus of physics at Pennsylvania State University, he was hospitalized April 27 after suffering a stroke while attending meeting here of the National Academy of Sciences. He lived in University Park, Pa.

Dr. Mueller joined the faculty of Penn State in 1952. He developed the field ion microscope, only one of his many inventions and discoveries, in 1955. It is the world's most powerful microscope.

Internationally known for his discoveries of field desorption, field ionization at surfaces, field evaporation of metals and fundamental effects in electron and atomic physics, he also had invented the field emmission microscope and the atom probe.

Dr. Mueller was born in Berlin and educated at the Technical University in Berlin. He worked as a physicist at the Siemens Research Laboratory there, where he invented the field emmission microscope that enabled him to photograph the surface of submicroscopically small metal crystals for the first time at near atomic levels.

He also was a division chief of the Kaiser Wilhelm Institute for Physical Chemistry. He was a professor of physics at the Free University of West Berlin just before going to Penn State.

He invented the atom probe after joining the Penn State faculty. The probe can focus on a single atom from thousands of surrounding atoms and identify it by its atomic weight.

Dr. Mueller, who retired from Penn State last year, was a member of the National Academy of Engineering and the National Academy of Sciences. He was a fellow of the American Physical Society.

The author of numerous articles in his field, he had received many major awards for his work.

He is survived by his wife, Klara Thussing Mueller, of the home; a daughter, Jutta Schwab, of Harrisburg, Pa., and two grandchildren.