DEBORAH ELLIS, whose prints have won prizes locally and elsewhere, has been concentrating upon watercolor paining for several years, gradually building skill and confidence. The esthetic returns are splendid in her solo exhibition at Gallery 4 in Alexandria. Ellis handles the medium with assurance; she has something to say, and she says it straightforwardly.

To make water a subject of watercolor paintings is a familiar conceit that Ellis handles unself-consciously in this show. The pictures in it ring variations on a single theme: cut flowers and plants (or in two cases, paintbrushes) in canning jars partially filled with water. The artist clearly took pleasure in observing and rendering the contrasting textures and refracted images; viewers will take similar pleasure in her skill.

Ellis has a knack for strong compositions. In this series she cleverly shifts the pieces from one picture to another, adding or subtracting jars or bringing them closer to the picture plane. In one especially weighty painting, stems and jar take up the whole rectangle of the paper; in others she makes adroit use of white space. The vivid images--frontal, shadowless and concentrated--suggest a hardheaded, elemental sort of confrontation between artist's eye and nature.

The artist carefully plots her pictures in pencil before applying paint to paper, even down to the delicate, sinuous, seemingly improvised tip of a dying leaf--an old procedure that works very well for her. The exhibition continues through July 9 at 115 S. Columbus St. The gallery is open from 10 a.m. to 5 p.m. Tuesdays through Saturdays. Stone Sculptures

Murney Kelleher's show of stone sculptures at the Athenaeum in Alexandria is installed to reflect the spare, dry grace of a Japanese garden. This is apt although, ironically, the installation is a bit overdone. "Yutzu IV," stretching the whole extent of a wall and made of brilliant red bunting and a few other odds and ends, looks extraneous, as if it were added simply to fill the space.

In smaller works Kelleher combines different materials effectively. Pieces titled "Koryo I and II," for instance, are delicate little abstract stage settings contrasting handmade papers with cut marble pieces and beautiful pebbles. "Silla I," which I found to be the most pleasing work in the show, is a simple confrontation of two rectangular pieces of stone, of similar mass and color although somewhat different in texture, balanced atop segments of bamboo stalks and arranged with two packages of chopsticks.

In these pieces Kelleher seems to have found a correct, intuitive balance between eye and artifice, between "found" and esthetically treated objects, between tension and release. Larger, more complex and perhaps more challenging pieces such as "Jerash" and "Yutzu V" do not quite attain the desired harmony. The Athenaeum, at 201 Prince St., is open from 10 a.m. to 4 p.m. through Saturday, closing day for this show. Anton Gallery's Summer Show

In its new incarnation the Anton Gallery on Capitol Hill is a welcome addition to the local art circuit (especially after the notable recent subtractions downtown). The reason is that the new owner, Gail Enns, has enlisted two professional artists as partners: Lindsey Hughes and Tom Nakashima. The result is a fresh esthetic policy as well as fresh paint and a general reconditioning inside.

"Preview 82/83," the gallery's summer show, gives a good notion of the new direction: no single artistic ideology, few recent master's graduates, fewer local talents and even fewer "big" names . . . but a lot of interesting art. Among the "featured artists" (who will have shows later this season) probably the best known is Will Peterson, the noted lithographer from Chicago, who lists on his re'sume' the fact that he was the real-life model for the character of Ron Sturlason in Jack Kerouac's novel "Dharma Bums." After that in the fame department it's clear sailing. Gus Sermas (Wilmington, Del.) is a painter who pushes the brush around at a terrific pace and with good results. His half-length female nude and his landscape-like pattern painting are lively, lush and luminous (as well as a few things that don't begin with "l"). Reid McIntyre (South Bend, Ind.) makes provocative, even scary, environment-type sculptures. Rob Barnard (Washington, D.C.) is an excellent artist who makes wood-fired pots. Reni Gower (Richmond, Va.) creates "paintings" from many layers of canvas, wire mesh, sandpaper and other things. With steel rods and elements of cast plastic Todd Slaughter (Columbus, Ohio) creates sculptures that extend precariously from the wall. The show continues at 415 East Capitol St., open Tuesdays through Sundays from noon to 5 p.m.