THE FREER GALLERY OF ART'S fourth director in five and a half decades of refined connoiseurship, Dr. Harold Stern, died Sunday at only 54. Dr. Sten was one of those important, somewhat unsung figures of the museum world withot whom the meticulous exploration and illumination of civilization's artistic resources would come to a grinding halt. His specialty was the Orient, and he was a logical choice to manage (since 1970) the country's preemminent repository of Oriental culture.

Like that reticent, austere gem of a gallery that he directed on the south side of the Mall, Dr. Stern did not play to the public. His primary responsibility was the tender care of roughly 12,000 objects - mostly from the Near and Far East. The collection is based on the matchless screens, scrolls, bronzes and jades bestowed upon the nation by Charles Lang Freer, the turn-of-the-century Detriot industrialist and headstrong explorer to the corners of the globe in pursuit of Oriental art.

During his years in charge of the Freer, Dr. Stern installed his share of public exhibitions. They usually sounded pretty esoteric to the ear (Japanese Ukiyoe paintings, Near Eastern ceramics, etc.). To the eye, however untrained, they usually turned out to be visual feasts. But, above all that, Dr. Stern held close to Mr. Freer's admonition in the deed of gift that the gallery be used for scholarly research and purchases to "promote high ideals of beauty." Much of his own research was on Japanese art, and his final work was a 1976 volume disarmingly titled. "Birds, Beasts, Blossoms and Bugs: The Nature of Japan."

In an interview several years ago, Dr. Stern discussed the Freer's role: "Certainly we are aware of our function as a museum in presenting public exhibitions. But there is also beauty in a person discovering and using his own mind, with assistance at hand if he asks." This was the way Dr. Stern ran the Freer. And we can all be grateful that he was usually - and devotedly - at hand.