"Masterpieces of Byzantine Icon Painting," an exhibition of a dozen small to medium-sized devotional images that went on view last week at Dumbarton Oaks, is a little show with a big impact.

The exhibit, consisting of nine loans from collections in the United States and England and three paintings owned by Dumbarton Oaks, is the first of its kind ever organized in the United States. It also marks the unveiling of the 13th-century icon of St. Peter, a rare Macedonian painting acquired by Dumbarton Oaks last summer at a price said to be between $250,000 and $500,000. Giles Constable, director of the museum, describes this picture as "the finest such icon in the United States and probably outside the Balkans."

Much of the show's impact is due to the unfamiliarity of the material. Icon paintings of this vintage--the images date from the early 13th to late 14th centuries--are extremely rare in this country. Initially, this creates a problem: It is impossible for eyes trained by Renaissance perspective and the ironies of modern art to adjust easily to these stylized holy images and become what Augustine described in the fifth century as "worshipers of pictures."

But it does not take long in the quiet gallery at Dumbarton Oaks, surrounded by other treasures of Byzantine art, to become aware of their very special presence. The current of religious emotion behind even the most stylized face makes it possible for us to understand something of the power the paintings once held for the believers who commissioned them.

The size and style of the St. Peter painting makes it stand out. It is the largest painting in the show, measuring 2 1/2 feet high and 1 1/2 feet wide. This indicates, scholars say, that originally the painting was prominently placed on the iconostasis, the screenlike partition separating sanctuary and nave in Orthodox churches. To raise money to pay for the picture, Dumbarton Oaks sold an 1899 Matisse painting and a Picasso watercolor.

In style the recently acquired picture is impressively realistic. The Apostle's long nose and intently furrowed brow are typical of the Byzantine formula and yet, almost as if the picture were a portrait, they strikingly suggest his worldly existence as fisherman.

Even so, the realism of this image is only relative. The saint's oblique gaze is inward-looking, spiritual; the swirls of paint used to model the head, hair and beard are elegant and abstract.

Byzantine art in all of its manifestations--architecture, painting, mosaic murals, ivory carvings, metalwork, manuscript illuminations--attests to an ordered, hierarchical, theocratic view of the cosmos. The most remarkable aspect of this art is its consistency of purpose over the centuries from the founding of Constantinople by the Emperor Constantine in 330 to the city's capture by the Ottoman Turks in 1453.

The little Dumbarton Oaks exhibition demonstrates this consistency, but it also suggests an expressive diversity. The show takes up only two display cases, but the range of both style and quality is quite broad, from the dry, linear stylization of "St. Spyridon," to the hovering spirituality of "Archangel Gabriel," to the realism of "St. Peter."

For an example of Byzantine art at its most refined, viewers simply need shift their eyes downward from "St. Peter" to an amazing mosaic depiction of "The Forty Martyrs of Sebaste." In this 14th-century miniature, 40 Roman soldiers (who died exposed upon a frozen lake rather than recant their Christian vows) are exquisitely rendered with bits of stone smaller than pinheads. Each elongated figure is much the same--the tiny picture is in itself an essay in Byzantine transmutation of the classic nude--and each is a little masterpiece.

The exhibition was organized by Susan Boyd, curator of the Byzantine Collection at Dumbarton Oaks, and Gary Vikan, associate curator for Byzantine art studies. They point out that even among experts, knowledge of the range of Byzantine icon painting has been limited for the simple reason that most of the earlier icons were destroyed in the fierce struggles between the monasteries and the iconoclasts during the eighth and ninth centuries.

This show is another building block in director Constable's campaign to open up and popularize one of the city's finest, and least known, museums. Dumbarton Oaks, located high on the Georgetown hill at 1703 32nd St. NW, is open daily except Mondays from 2 to 5 p.m. "Masterpieces of Byzantine Icon Painting" will remain on view through June 26.