Seven years ago. Milwaukee-born artist Tom Dineen was in the army toiling away in the graphic arts section of the Pentagon. But after seeing two of his paintings in a show at the Alexandria Art League, dealer Louis Andre of Wolfe Street Gallery gave him the first of what were to become annual one-man shows.

Now, at age 30, and after six solo exhibitions, Dineen has a devoted following of collectors and his shows regularly sell out. Why? I think that collectors perceive Dineen as being one of the younger Washington artists who have a chance to make it big," says Andre.

Apart from his extraordinary prolificacy and ability to change. Tom Dineen's shows are marked by an extraordinary fact: Each one seems to represent a complete cycle of work in which a challenge is presented taken up and resolved often in a rousing, surprising conclusion.

His new show at Wolfe Street Gallery is no exception. It begins where the last one left off with a cycle of charcoal drawings in diptych and triptych formats involving gigantic sheets of white paper upon which Dineen's sleek satiny-surfaced and rather threatening biomophic forms continue to disport themselves in virtuous compositions.

But in a drawing which seems to be the climax of this current cyde, a new and welcome richness and complexity of subject matter is introduced. Two of these seemingly living breathing bimorphic "presences" connected by an unbilical cord, stand before what appear to be three Dineen drawings inn process each covered with a flurry of short impressionistic strokes of pastel color. The subject matter is clearly Dineen contemplating what is currently going on in Dineen's own art - the reintroduction of color and a much needed breath of fresh air. The piece is surely the most profound in either this or last year's shows.

This exhibition ends, not surprisingly, in a surprise, a large triptych filled with the flecks of color fore-shadowed in the earlier drawing. It is almost as if someone had turned on the light in the dark closet where Dineen's presences had been hanging out. One such "presence" (no doubt the artist's alter ego) seems taken aback at finding itself in this color and light-filled space, and, for once, seems menaced rather than menacing.

The space itself, however, is filled with glassed and mirrored ambiguity. Tune in next year for the surprising conclusion of Dineen's next challenge.

Finding ways to express movement within the single frame of a still photograph is a challenge many thoughtful contemporary photographers have been setting for themselves among them Margot Kernan, whose new show has just opende at Foundry Gallery, 2121 St. NW. The series of 24 casual and often intimate domestic episodes is entitled "Moving Pictures," and at their best they are moving in every sense of the word.

Kernan is both filmmaker and still photographer, and her mastery of both techniques has given her work a distinctive (and seemingly instinctive) ability to capture the instant and gesture which implies not just the slice of time when the shuter was opened, but the whole span in which the ongoing episode or event took palce. A poet of the prosaic, she also manages to capture the enveloping mood.

Kernan uses the deliberate blur to imply movement, but only to reinforce her intent. She does not make the mistake of depending wholly upon it. A splendid example is the third of a series called "Watching The Godfather on Television," wherein two figures rise, probably at the onset of a commercial, to rush off for refreshment of one sort or another. The viewer's identification with the figures in the photograph is so complete that the muscles tense. In another example, her subject matter is a vibrating, pulsating "Light Ray in the Hall," which actually seems to move.

But "moving" has yet another meaning in Kernan's work, easily discerned in the touching photograph of her parents in their New Hampshire home, her be-robed father smiling lovingly from beneath the portrait of an ancestor. Kernan's range is wide and she only falters when she seeks to construct her own symbolism, as in her implied re-birth in the form of a self-emergence from a bathtub.

Susan Middleman, whose simplified, higly patterned figure paintings had become rather mannered of late, is also showing new work at Foundry Gallery, and she has taken a big step forward, both in terms of self-confidence and profundity.

In two black-and-white drawings, entitled "The Cigarette Smoker," bold pencil strokes reinforce a bolder design, and reveal a new interest and ability to deal with character rather than caricature - surely a giant step. The same growth can be seen in the striking painting entitled "Marimekko," where the "cartoony" aspect of earlier work in entirely gone. Through Oct. 21.

Most artists find it difficult, if not impossible, to know their best work from the less worthy. It is like asking them to choose between their children. It is thus an important function of the gallery director to make such choices (often against the artist's will) and to show the artist only in top form.

The need for a good weeding of Helen Herzbrun's current show at Jack Rasmussen Gallery, 313 G St. NW, comes close to obscuring the strength of her best new abstract painting. Concerned primarily with cremating the illusion of space through composition and transparent planes of color, Herzbrun here manages to do so with ease, such ease, in fact, that several of the paintings, and most of the drawings, seem too hastily arrived at. So well informed is this artist's understanding of both composition and color that she neither pleases nor challenges it.

Herzbrun's strong suit is her expressive way with color, and it is when she subverts the "push-pull" spatial considerations to the larger goal of expressed mood that she best succeeds, as in "Counter Plane," a worthy descendant of Nicholas de Stael without the impasto. In "Bent 1978" the increased looseness and directness of these recent works has been disciplined into a delicious small painting which has, incomprehensibly, been hung in the back. Through Nov. 4.

Rudy Ayoroa is showing new sculpture and paintings at the tiny Huber Gallery, 1214 St. NW. Most engaging are the small lucite boxes-containing reflective mylar and tubes and strips of luminescence and perpetual motion. The colors and shapes seem to move and are constantly transformed a the viewer moves or turns the sculptures in the hand. If Brentano's were on their toes, they'd commission an edition quick, intime for Christmas.

Meanwhile, Ayoroa has made his own, very small editions of 5 or 10.

While these tiniest works have an adult toy-like quality, the wall-hung piece No. 1 is even more fulfilling, and it is easy to imagine it on a larger, architectural scale. All of these sculptures have a warmth and delicacy which belies the space-age plastics from which they are made. The paintings, however, which are solid, op-like designs, fail to go beyond mere elegance and complexity of design into something more satisfying.