THE Islamic Center on Massachusetts Avenue may not stand serious esthetic comparison with the great monuments of Moslem architecture ranging from Spain to India, but the modest, elegant little building with its trim minaret that towers over Rock Creek Park has added an appreciable grace note to the city's architecture for 26 years.

During its recent trials the pacific, benign image of the place was shattered repeatedly, of course. The damage was also physical.

The treasured Minbar, a pulpit made of 10,000 elaborately carved segments of wood, joined by Egyptian cabinetmakers without benefit of nails or glue, was torched by an arsonist. The Turkish tiles in the prayer hall, with their luminous blue and turquoise colors, were covered with grit. The plasterwork on walls and ceilings, brilliantly painted in a complicated network of calligraphy and decorative motifs, was severely damaged by water leaks. The beautiful stonework of the exterior, long in need of a cleaning, gave the place an unwanted look.

Not so today. Except for the Minbar, which has not been replaced, the building wears its original sparkle inside and out. The restoration was accomplished during 14 hectic weeks in late spring and early summer under the direction of Washington architect Mokhless Hariri, president of the Georgetown Design Group.

"If someone had told me years ago, when I was studying architecture at the Ecole des Beaux Arts, that I would be so heavily involved in Moslem architecture, I'd have thought they were crazy," he said the other day, while surveying the praiseworthy results of the artisans' work in the center's prayer hall. "And if someone had told the members of the board of governors that we'd finish the job on time, they wouldn't have believed it," he said. "Two weeks before the opening in early July the place was filled with scaffolding and the smell of plaster."

The building, conceived during World War II by A. Joseph Howar, a Palestinian immigrant who had settled in the Washington area in the early 1900s, was designed in Cairo by Egyptian architects and executed here by a local firm, Irving S. Porter and Sons. Its style, Hariri explained, is a harmonious blend of Islamic traditions.

The basic exterior proportions and the form of the minaret are Middle Eastern, primarily Egyptian, he said, while the tiled porch roofs that extend from the symmetrical wings reflect Spain's Andalusian influence. The only Western element is the way the building respects its surroundings by being set back from Massachusetts Avenue. "In the Islamic world the mosque is much more directly related to the city streets," Hariri said.

The courtyard behind the arched entranceways is one of the more entrancing small open spaces in the city. This is due in part to the fine proportions of the arched arcades and the exquisite blue decorative motifs above the arches, and also to the subtly spellbinding curve of the sidewalls--convex on one side, concave on the other. The walls were formed this way to accommodate the alignment of the prayer hall, which was set at an angle, towards Mecca.

This harmonious blending of elements continues inside the prayer hall, a cube with symmetrical columns surrounding an octagonal dome. The tilework that rings the hall reflects Turkish and Iranian precedents, while the painted decorations of the upper walls and dome, more geometric and colored in strong yellows, reds and earthen hues, recall Umayyad architecture, a more ancient style born in Damascus.

One of Hariri's discoveries during the restoration was a long-forgotten inscription, discretely placed in a corner of one of the columns in the prayer hall: "This is the ornament and the calligraphy of Abdel Hassen and his assistants, Mohammed Mehdi and Toufik Ahamed." These were the Egyptian craftsmen imported to do the work in the 1950s. In its modest way this signature says a lot about the impressive, ancient visual culture of Islam, and about the spirit in which the Islamic Center was founded.

The center is located at 2551 Massachusetts Ave. It is open to visitors of all faiths from 9 a.m. to 10 p.m., seven days a week.