The National Aeronautics and Space Administration records the undistinguished-looking piece of basalt as "Piece 230 of Apollo 11 rock No. 10057."

But for the Washington Cathedral, the 3 1/2 billion-year-old silver dollar-sized slice of moon rock is the crowning glory of a spectacular blue-toned stained glass window commemorating the exploration of space.

The rock, plucked from the Sea of Tranquility in 1969 by the first man to set foot on the moon, was leaded into the window yesterday.

It rests at almost the center of the 19-foot gothic window, whose designs was inspired by photos brought back by early space flights. In velvety shadings of blue, the window design suggests planets in a night sky flecked with stars. A tracery of red around the edges gives promise of the rising sun.

The window, designed by Rodney Winfield, was installed in July, 1974, with a circle of black paper between the two layers of glass as a stand-in for the actual moon rock.

With scaffolding still in place for construction of the adjacent walls, cathedral officials feared their lunar artifact might prove too much of an attraction for vandals if it were set in place at that time.

So the rock in its plexiglass cradle was kept in the cathedral's vault until yesterday when Dieter Goldkuhlie, whom cathedral works director Richard T. Feller described as "the best stained glass man in the country," pried out the blank and worked the precious disk into place.

Goldkuhle's two sons, Andrew, 10, and Guido, 11, stayed away from their classes at Lake Anne Elementary School in Reston to watch the historic occasion and hand their father tools and cups of tea from a silvery vacuum bottle.

The cathedral's moon rocks is the only one given by NASA to a nongovernmental institution, according to Dean Francis D. Sayre Jr.

Hovering paternally around the work site, the dean shared an encounter with the treasure with a favored few. "Hold out your hands and hold a 3 1/2 billion-year-old rock," he told a white-haired staff member.

Obediently she cupped her hands and gazed, awe-struck, at the disk the dean placed in them. "My grandchildren will be so impressed," she exclaimed as she carefully handed it back.