Washington's Mark Leithauser is the best etcher in town. His extraordinary prints, now at the Hom Gallery, 2103 O St. NW, suggest a young Old Master.

He dreams the dreams of youth, but his technique is antique. Leithauser is 31, and some aspect of his age is apparent in his landscapes, especially his early ones. Their woods are full of wizardries. Their twisted trees and twining vines suggest the haunts of hobbits. Gnomes with pointed ears mutter in the ivy of "The Journey Is the Teacher," a print that he completed at the age of 22. These early prints of Leithauser are, at least in imagery, familiarly fantastical. Other artists here have dreamed comparable visions, but none has made such prints.

At etching he's a master. His prints are small and quiet, they do not yell, they whisper; they have the scale of the page. With burin, copper plate, etching press and acid, black ink and white paper, Leithauser can conjure a thousand shades of gray. His prints are filled with distances, with mist and dappled sunlight. His details are remarkable. We see every twig of every tree, the softness of the moss, the antique-silver bark of the fallen elm.

Leithauser's technique is entirely traditional. Unlike other subtle modern etchers, for instance Peter Milton, he does not draw on acetate, does not use the technology of the photographic plate. He doesn't use aquatint, either. His fogs and mists are stipplings of microscopic dots. An early print at Hom's, "Horological Fascination" (1974), portrays a medieval clockmaker, a maker of automata, happily surrounded by tools and fraying ropes, weights and cogs and wheels, busy at his bench. A grandfather of Leithauser's repaired antique timepieces. The artist, too, accomplishes amazing things in metal. He works his copper plates (one of which is on display) with a jeweler's patience and a clockmaker's delight.

His prints are dense with time. Very slowly made, they should be slowly seen. Leithauser might spend a year on a single image. He begins with little pencil studies (some are on display and all are done from life) of a vine, say, or a tree trunk or a group of ferns. These most delicate of drawings become the scattered seeds from which his etchings slowly grow. The evolution of his images may be traced in this exhibit by the trial proofs on view.

Leithauser, who makes his prints at home, is assistant chief of design at the National Gallery of Art. He works with masterworks daily, and his familiarity with quality is apparent in his art. His newest prints -- "Birches" (1980), and "The Little Pigeon" (1981; a moonlit image named for a river, not a bird) -- are free of trolls and mice that chat. His magic has grown subtle. His show runs through the year.

Howard University

Art that is political is frequently hamfisted, but Jeff Donaldson's is poignant. His 20-year retrospective at Howard University manages to be at once delicate and fierce.

Donaldson, in the early 1960s, helped paint Chicago's Wall of Respect; he was one of the founders of the group called Africobra (for "African Commune of Bad Relevant Artists"); he celebrates the warrior, and the usually idealized heroes he portrays often appear armed with automatic weapons. He paints to rouse his people, and to stir the blood.

"It is very dangerous," he's said, "for art to be accepted or supported by an alien audience, an audience for which it is not intended." Many viewers will not smile at the gray pot-bellied cop in his "Aunt Jemima Burnin' " (1963-64) or at the .45 pistol pointed at the white South African official in his "Visit Azania" (1974). But one need not be black to feel the sweetness that is wreathed around the fire in his art.

Donaldson paints beautifully, rhythmically, melodiously. Most of his compositions are rigidly symmetrical, but their rigidities are softened by the twinklings of his filigrees of color. He works with little brushes and countless dots of subtle color; he uses gold and silver and a hundred other hues. The most moving of his paintings may be the deeply loving, deeply proud, portraits of his parents. His father, Frank, was a railroad fireman; his overalls are silver and his hat shines like a crown. Jeff Donaldson's portraits often look like icons. He sanctifies his subjects. Dissolving, lacy haloes surround his heroes' heads.

It is often said of Donaldson that he paints propaganda, but his show leaves one believing that he paints religious art. His devotion to the sacred is most clearly seen in his gleaming and collaged and nearly apolitical newer works on view. Donaldson is a professor at Howard. His show there closes on Jan. 8.

Gallery K

The goddess of the cats has never been so busy. She has cunningly inspired the current exhibition at Gallery K, 2032 P St. NW. The show is full of cats -- tabbies, Persians, mousers, Maine Coons, Siamese. And panthers, too, and lions, and purple cats and black cats, cats of all descriptions. They purr, they meow, they stretch and leap to the attack. There are more than 50 works on view, by 30 different artists, and there is a cat, or cats, in every object on display. Patricia Buck's leaping multicolored cat is among the prettiest; Sidney Lawrence's "Catmandu" is the biggest; William Shirley's "Small Cat," a wonderful little portrait painted in poured polyester, is the most impressive. The cats will be at Gallery K through Jan. 10.