SINCE BEFORE the dark ages, stained glass has transmitted and transmuted light in marvelous and mysterious ways.

In medieval cathedrals, stained-glass windows gave mortals sitting on hard seats a glimpse of the glorious light of heaven.

Authorities presume the art of architectural stained glass goes back to antiquity, though its origin is lost. The best-known existing examples are the 12th-century windows at St. Denis, Chartres, Bourges and Poitlers, France; Canterbury Cathedral in England and Strasbourg in Germany.

During the 19th century, stained glass came down to earth for use in the home. Sparked by the renewed interest in medieval tradition, much good work was done by William Morris of the English Pre-Raphaelites who triggered the Arts and Crafts movement.

Fanlights above the front door, insets in and around front windows and doors and portholes on the stairs were embellished with colored glass framed with lead. Ruby, emerald, topaz and other gemstone glass also ornamented furniture, including the famed Tiffany lamps, as well as weathervanes, cabinet doors, inkwells and a myriad more objects.

Today, once again, stained glass has become a part of the general scene - especially in California, where the light is especially brilliant (on non-smog days of course). The West Coast stained-glass enthusiasm seems to have really gotten well under way about two or three years ago. In Washington, perhaps, the stained-glass revival resulted from the rowhouse remodeling fever. The taste for stained glass results from more than nostalgia. Translucent glass catches and seems to magnify the small amount of light available to the rowhouse. On a crowded urban street the colored and patterned glass blocks out the view of an objectionable high-rise or the neighbor's garbage dump.

The colors can be tricky, sending rainbows across the floor, changing interior color schemes, flushing people's faces with red. The effect changes every minute or second, as clouds pass over the sun and the moon waxes and wanes, or the street light flickers and goes out.

The art of stained glass is changing. Traditionally, an easel artist designed the cartoon or master sketch to be executed by a stained-glass craftsworker. Today, the stained-glass artist is most likely to be his own craftsman, or at least he works along with his staff is putting the pieces together.

The Renwick Gallery has just opened a show (through Feb. 19) portraying the stained-glass maker as an independent artist, free of the constraints of the door frame or the window sash. Here the emphasis is all on the design. But the artists are also revealed as technical innovators. Sandblasting, double and triple glaring, applied lead lines, sheet lead, lenses, shaped metal armatures, photographic processes, painting and mirrors are all used today - sometimes all in one piece. What artists/craftsmen are getting away from is the 10th-century efforts to paint on stained glass, instead of putting together the design out of units of glass.

The works are intended to be hung as paintings (they must have backlighting) in a serious way as the works of art they are. But as art they are more than painting because they have a depth not possible with paint and canvas.

Most of the pieces in the Renwick show owe great debts to the hard edge painting trends of our day. Pop, op, surrealism, expressionism, realism, cubism, abstractism - all these are found as influences on the work.

Lloyd Herman, director of the Renwick Gallery, is to be commended for adding Sal Fiorito of Washington, S. Gilberson Prewitt of Alexandria and Randy Swell of Bethania, N.C., to the 10 artists chosen by the organizer of the show, the New York Museum of Contemporary Crafts. The Contemporary Crafts Museum too often overlooks artists/craftsmen working from Washington and the South.

The southern works are as good, if not better, than any of the others in the show - pointing out the truism that it is not enough to be from the West Coast, you must also have talent.

Sal Fiorito's studio is just off Dupont Circle. His stained-glass pictures have been seen here at the WPA gallery on F Street NW. One of his most interesting works in the Renwick show is made of many different kinds of leaded galss: mechanical glass, German, French, antique glass and prism. The design is alternate stripes or rather bands with an inset shaped like a man's profile. The cross hatchings of the mechanical glass makes for unusual effects. A more realistic piece of his, almost a fool-the-eye, is a joke about stained-glass windows. It looks as though it were a blind with a pot of flowers in front and a plant behind. He has taught a good many classes in stained-glass work for the Smithsonian Associates.

S. Gilberson Prewitt's studio is in the Torpedo Factory in Alexandria. She is represented in the show by "Male" and "Female," anatomical abstractions that play with dark and light, shapes and colors.

Both Fiorito and Gilberson Prewitt make a living at their work, though Prewitt admits "it's always feast or famine." Both have studied stained-glass work abroad in England. Prewitt also has studied in California; Fiorito in Germany. Both studied with the great Ludwig Schaffrath in Berkeley, Calif. Neither began as a stained-glass artist. Fiorito majored in biology at Catholic University. Gilberson Prewitt was an art major at the University of Maryland.

Many new restaurants and ice cream cafes have learned the uses of the material. Recently, Fiorito was asked to do a transom for an office. Currently Fiorito is working on a new ice cream parlor in Fairfax with sort of neo-art nouveau designs, and is negotiating with Garfinckel's on a skylight. Gilberson Prewitt has done a number of architectural works with spectacular results - a 16-foot window for architect Bill Brandson's townhouse off Dupont Circle and two French doors for lawyer Leonard Ball.

The work time on these pieces varies enormously with the degree of complexity, and the availability of the glass. Gilberson Prewitt did the Ball commission in two months. The Brandon commission took two years.

Prices for both Fiorito and Gilberson Prewitt range from $275 or so for a small work, on up, up, up and up. Gilberson Prewitt says her price is roughly from $45 a square foot, depending on the glass and complexity. Fiorito says each work has to be considered on its own. Both largely work on commissions, though occasionally they produce the independent works such as the ones at the Renwick.

Fiorito works this way: First the artist does a sketch of the work. The cartoon is then blown up to size, perhaps even colored. If it is an architectural piece, the cartoon is tried in the spot where it is to go. The artist makes a cutting pattern, which is laid on a light table, with the glass sheet on top. The glass is then cut with an ordinary glass cutter. The glass sections are put together with an extruded lead channel. The lead is heated with a soldering iron. Then it's puttied in with a black cement, and reinforced every eight inches or so with reinforcing bars. The work is then framed or installed in an architectural frame.

The Renwick show includes the work of 13 artists/craftsmen exhibiting 43 works. Paul Marioni's "Dali 1972" uses glass, lead, fresnel lenses and leaded stained glass to make an astonishing portrait. Richard Posner uses glass, lead, cibachrome transparencies, sandblasted glass and copper foil to produce a mysterious story/picture called "The Big Enchilada, 1975." Ray King's "Bird Piece 1976" and Peter Mollica's "Untitled III" are great examples of geometric designs emphasizing color.

A few of the pieces, unfortunately, seem merely self-indulgent. Robert Kehlmann, who wrote the interesting and informative introduction to the show's catalogue, is represented by a work that looks as if it were made by throwing a rock at someone's window. Another by him seems equally chaotic. And Sanford Barnett's works look as though they were made in kindergarten with fingerpaints on glass.

It's hard to keep track of all the people now making stained-glass works in Washington. A year or so ago the Greater Reston Arts Center held a show of artists in stained glass. In it was Rowan LeCompte, a Northern Virginia artist who is responsible for many of the windows in the Washington Cathedral, including the great 15-foot, 11-inch rose window installed in 1976. Dieter Goldkuhle, another Reston artist, also has made windows for the Washington Cathedral as well as restorations for the Cloisters and the National Collection of Fine Arts. Jeff Powley of Chevy Chase has made a number of interesting commissions, including an inset in a garden wall for botanist Tom Sodestrom on Capitol Hill. Gary Turner and Bruce Helms of Hollin Hills reproduce Frank Lloyd Wright designs in stained glass. Many people noted the FLW stained glass in the Renwick Gallery's recent Wright decorative objects show.

In the catalogue Kehlmann writes, "Ultimately it is the delicate interplay of light, glass and lead - the substance of stained glass to which we respond. Such a combination of the material and the immaterial, in one form or another, lies at the core of all artistic expression."