A major public sculpture commission can make a profound difference to an artist, not only by broadening his reputation, but also by nudging his art into new directions.

A notable case in point is that of Washington sculptor/photographer William Christenberry, whose new show at Middendorf Gallery represents not only the first substantial group of wall pieces he has ever made, but also the exciting marriage of his longstanding interests in sculpture and collage with his newly revived interest in painting.

The 11 painted, collaged wood panels in this show -- some huge, some on a more intimate scale -- grew directly from the challenge provided by a 1978 General Services Administration commission to create a 32-foot-long "Southern Wall" for the lobby of the federal courthouse in Jackson, Miss.

"When I was asked to compete for the commission," says Christenberry, "I told them I hadn't made wall pieces -- that all my work, apart from photography, has been three-dimensional, such as the 'Southern Monuments.' " (Like his better-known photographs, these little buildings with peaked roofs shaped like Ku Klux Klan hats are devoted to evoking the vanishing South and were seen in "Southern Views," a major Christenberry retrospective held at the Corcoran in 1983.) "But when I made the maquette, all of a sudden I could see the possibilities for wall sculpture."

Such possibilities snapped into focus when Christenberry decided to insert into his "Southern Wall" a large section of metal collage made from cut-up segments of his vast, beloved collection of faded old metal signs: Coca-Cola, Nehi, cigarette and Champion Spark Plug signs and Alabama license plates, mostly scavenged on annual summer visits to his native Hale County, Ala. He had often used such faded signs in his photographs and plastered them on the outside of his sculptural buildings, but he'd never cut them up. Now, attacking the lesser of them with a pair of antique tinsnips, he put them back together in a patchwork crazy-quilt collage that, in itself, reminded him of an old quilt back home.

He's been at it, on and off, ever since, executing other commissions, including the smashing, 12-foot-long, 3-foot-tall "Washington Wall" that opens this show. Commissioned by a Washington law firm -- and so named because it includes a bit of a Washington, D.C., license plate -- "Washington Wall" also includes some small squares cut from asphalt roofing shingles, roofing nails and other building bits left over when a garage adjoining his Washington home was torn down to make way for a studio last spring. A tall, uncannily handsome section of partly rusted, partly shiny corrugated metal from that garage serves as the central element in another outstanding piece in this show, titled "Wall Construction V."

But it isn't just the use of materials from someplace other than Hale County that makes this show important and remarkable: It is the new painterliness and the open, personal expressiveness that shows up in the best works. The show seems to divide into two parts: the tighter, more literal pieces, in which most of the surface is covered with highly organized areas of metal collage (such as "Alabama Wall I," which is encrusted with bits of Alabama license plates); and the looser works, such as the aforementioned "Washington Wall," and "Wall Construction V" and "Royal Wall." In the latter group, open expanses of painted color play a major role, and across their surfaces we feel a direct sense of the artist's hand at work in the intuitive placement of a bit of wood lath here, a bit of red paint there, or a smattering of roofing nails and grommets.

If the looser works represent the larger, bolder leap for Christenberry, all of the works on view are superbly made and show his nimble mind at work: his use of entire loaded words, such as "live," or "refresh," or of witty bits of words, that now read "da" and "no." There is a clear mastery of formal, organizational matters, and an interest in implying deep space through the manipulation of his cut-out words, letters and signs. He takes obvious sensual pleasure in the calligraphy of a Coca-Cola sign, which he cuts up and uses as pure, curving line.

The works function on many levels: as evocations of place, as well as of humor, and as formal compositions of color and texture, fresh and weathered. There are echoes of Diebenkorn and Rauschenberg, artists Christenberry openly admires. As to the matter of collage, however, a few of Christenberry's large color photographs of rusting, corrugated metal barns with their rectangular patches of varying shades of rust, are included in this show and vividly reinforce his longtime interest in the collaged surface.

"I wouldn't be reluctant to say that there may be more painting in the future," says Christenberry, who is delighted in the way these works, all completed since last June, have brought together so many of his artistic concerns. He is reluctant, however, about cutting up his beloved signs.

"I've only cut up one or two where I've had some regrets," says Christenberry, who makes clear that his finest signs, which cover the walls of his home (and exhibitions) in great profusion, are not and never will be destined for the snippers.

"I'm excited about this direction," says Christenberry. "I feel this has opened up all kinds of avenues for future work -- if I can just keep the materials rolling in."

His show will continue through Jan. 4 at Middendorf Gallery, 2009 Columbia Rd. NW. Hours are 11 to 6 Monday through Saturday.