Alfredo Halegua, the Uruguayan-born Washington sculptor, has not been seen or heard from much in five or six years. The reasons why are dramatically apparent in the exhibition of new works he has mounted in the shaded yard of his home in Northwest Washington.

There are 10 pieces in the show, each a thoroughly accomplished variation upon his familiar geometric themes, each huge, each fabricated from heavy plates of steel. To make them Halegua did not send drawings to a factory. Instead, he transported the factory to his house, bringing in welders and cranes to assemble and place the pieces under his own eye.

Another dimension of his work is the setting itself, a stunning terraced sculpture garden under a high canopy of trees. Halegua built that, too, converting a gully to a garden with railroad ties and a hundred truckloads of dirt transported from the construction dig for the Post Office building on Wisconsin Avenue. Quite a few of the sculptures have been sold but it is hard to believe they'll ever look so good as they do now as a group, their crisp planes echoing each other under the softening green.

Halegua is a born sculptor. In a way the story of his art is as simple as that. Everything he makes feels right in three dimensions, occupying space and changing it at the same time, implying a sense of movement and constantly beckoning the viewer himself to move round the work, to experience its many facets. This is abundantly clear in the mature works but it can be felt even in a Cubistic reclining figure (with its Henry Moore bone face) that the artist carved shortly after emigrating to the United States in 1959.

When Halegua adopted an abstract, geometric vocabulary in 1968 (stimulated by an invitation for a solo show at the Baltimore Museum) his debts to European constructivists and American minimalists were clear, although even then important differences were apparent. In contrast to the hard polemical style of most of the North Americans, Halegua's work was urbane, intuited, effortlessly sophisticated.

And so it remains today. His forms are big, hard, sharp, emphatic --but they're also somehow easy to take--gentle, alluring, surprising. In "Red Tango" he does the simplest thing: he takes a narrow square box of steel, almost as flat as a painting to begin with, bends it on the dividing diagonal, and punches a rectilinear hole in it. The result is a game of perception. He does similar things with cubes, oblongs, plinths and other, more idiosyncratic forms.

It is an art of sensibility more than innovation, intuition more than logic, and it looks terrific on its home grounds at 2601 30th St. NW, where it will remain on public view through May 30. The garden is open from 11 a.m. to 5 p.m. Thursdays through Sundays, or by appointment (telephone 332-7460).

Nyangoma's Gallery

Winifred Owens and Malkia Roberts, artists who share an office as teachers at Howard University, are sharing an exhibition of their works this month at Nyangoma's Gallery, 2335 18th St. NW. As different as they are in form and materials, the works go well together. Owens is a ceramic sculptor. Drawing on a variety of African, Oriental and American sources, her expertly made stoneware and earthenware pieces are witty, inventive, pointed and good to look at. Malkia is a painter. Drawing upon a similar variety of sources, her paintings, with figures weaving in and out of a densely layered fabric of brushstrokes, are persuasively exultant if not uniformly fresh. Through May 15, open Wednesday through Sunday, noon to 6 p.m.

Along P Street

Along P Street near Dupont Circle, a wide variety of sights, sensations, styles: Hayes Friedman takes on the awesome subject of the Holocaust at the Haslem Gallery with the best paintings she has made to date, where we experience the horror through a quiet indigo penumbra (through May 22 at 2121 P St. NW, open Tuesday through Saturday, 11 a.m. to 6 p.m.) . . . At Henri's, sculptor Lawson Smith, in his fourth solo show there, continues obsessively to wrap things in tight, bright bundles of thread. This year it is Victorian architectural relics that he partially wraps, and it is perhaps an idea that is wearing thin (through June 2 at 21st and P, 10 a.m. to 6 p.m. Tuesday through Saturday) . . . Across the street at Gallery K, Maureen McCabe makes another appearance with her uniquely fine-grained brand of hocus-pocus in feathery tableau-like pictures assembled with dime-store detritus and lots more. Andrew Krieger's funky surreal boxes containing cut-outs of his own delicate pencil-drawings share the space (through May 15 at 2032 P St., open Tuesday through Saturday, 11 a.m. to 6 p.m.).