Washington artist Stanley Sporny has had a very good year in which his large, deliciously painted landscapes--with their high horizon lines and vast spaces--have made their mark in several group shows here.

Sporny's new solo at Osuna--his first since 1979--suggests that he's trying to speed things up to satisfy the growing demand, and it doesn't always work. There are strong paintings here, but they tend to be those we have seen before--notably the panoramic view over smoggy Los Angeles titled "L.A. Air." The Southwest desert scene called "Adobe Abode" and "Stacked Haybales II" also show to good advantage the artist's skill at conjuring the special light and atmosphere of a place. But there are other works--"South Dakota Farm" in particular--that give the distinct sense of a painter working faster than he should.

You can't blame him. Sporny's chosen medium--thickly painted oil with broad, juicy strokes that sparkle with real light--take days to paint and days to dry. No wonder, then, he has tried a sketchier form of rendering in "Up Country--Sri Lanka." It is also no surprise that he has tried swifter media, such as pastel, and has borrowed compositions from himself, repeating them in smaller, more saleable, and generally less satisfying formats.

It is possible, of course, that a search for greater speed played no role in the tossed-off appearance of some of these works, though they surely left this viewer with that impression. Nonetheless, Sporny is a fine painter whose career is clearly just beginning to take off.

Also on view at Osuna is the unusual work of Charles Bessant, who combines molten resin and brass into sculpture that has the look of giant modern jewelry. Using casting and inlay techniques, Bessant manages to transform the clear, slick medium of resin into what appear to be aged, pockmarked chunks of semi-precious stones or marble. The configurations are elegantly abstract, in the manner of much contemporary Latin American sculpture, but they use the opacity and transparency of the resin to good advantage. Both shows continue at 406 Seventh St. NW through July 17. Hours are 11 to 6, Tuesdays through Fridays; closed Saturdays. An Owner's Show

Slavin Gallery, 404 Seventh St. NW, is showing one of its best artists to date: owner Jym Slavin.

Howard Mehring inevitably comes to mind in this show of stain paintings, as layered dots of color drift and zoom around the canvas. Two works even have some of the subtlety and serenity of Mehring, namely the pastel "New Life" and "Waiting." Overall, however, a rather raw, experimental quality prevails.

But the energy is winning, even when it seems to suck the colors into a too-obvious vortex at the center of the canvas. Slavin is still a very young painter, and he has come a long way since his rather tentative, textured abstractions of the late '70s, examples of which are on view. He--and his gallery--will be interesting to watch. The show, which also includes some amusing--if rather mannered--bronze sculptures by another Washington artist, Mark Kramer, will continue through July 13. Hours are Tuesdays, noon to 4, and Wednesdays through Saturdays, noon to 6. 1221's Final Show

Gallery 1221 Inc., a gallery touting "black investment art," is having its final show at 1221 11th St. NW after only six months in business. According to Gallery 1221 corporation chairman, attorney James R. Haynes, the gallery will relocate in the fall, although where has not been determined.

The gallery, which has held three exhibitions (notable among them "6 Black Giants"), has a long way to go toward making itself more professional, as is amply illustrated by an apallingly bad show of seascapes in the back room--the sort of work that used to be seen in department store art shops. But it has also made a contribution, by introducing the work of Washington painter Charles Sebree, for example, and by giving added exposure to good artists such as Washingtonian Richard Dempsey. Currently run by a board of directors, the gallery--if it does reopen--might do well to consider more experienced management.

A few of Dempsey's abstract expressionist watercolors from the mid-'70s--given fuller treatment in a large show at IMF just a few months ago--are now the featured show, and they underline this Washington artist's lyrical way with expressive color. "Growing Plants at Night," with its splatterings of shifting blue and purple and mauve, is an especially satisfying example, as is "Ebony Sprin Metamorphosis." Dempsey is also showing some newer works, made with felt-tip pens and collage, which involve themselves with the mysterious imagery of astrology. They suggest a potentially interesting new direction. The gallery will be open today and next Saturday, noon to 5, and next Tuesday and Thursday from 12:30 to 6:30. The show--and the gallery--close July 10.