ALEX CASTRO, a local artist with a degree in architecture and an affinity for theoretical physics, hopes to have his Hollow Press extend printing beyond publishing into art - to work with artists to produce books that are "an alternative to the gallery wall" and "to allow what a book is to join hands with what art is."

When not teaching art at George Mason University, he works mights and weekends to finish Gardens, with photographer John Gossage. With 24 original photos and texts chosen by Walter Hopps, curator of Twentieth Century Painting and Sculpture at the National Collection of Fine Arts, it will be bounded by Donald Etherington, specialist in binding and restoring rare books at the Library of Congress. Limited to 20 copies at $2800 apiece, it will be first shown at an opening at the Leo Castelli Gallery Uptown in New York on February 11. Bargain Basement Printing

NOBODY EXACTLY KEEPS count, but Washington is thought to be third in the country - after San Francisco and New York (and just ahead of Iowa and Vermont) - in the home basement printing field. Small publishers around town can cut their printing costs by doing their own, and the Writer's Center in Glen Echo Park has a Compuragraphic 1V typesetter (for offset printing) with 15 or 20 different type faces, ranging from six point to 36 point, plus a copy camera, a plate maker and a Multilith (offset) press - and offers a course in how to run them all. (For next January's course, call Kevin Osborn at 229-0684). "We're a resource for people who want to express themselves in print," Osborn says.

But the true believers among home printers are letter press men (and sometimes women). As the old print shops fold in the face of bulldozers and computers, a bush telegraph alerts the faithful that another Chandler and Price, or a full set of Caslon or Garamond is about to come up for grabs, and another unwieldy crate is added to the household stock. Today's amateur recruit is tomorrow's serious pro.

Stan Nelson of the Smithsonian's Graphic Arts Division is not only a home printer on his own time, but designs and casts his own type, using the ancient 15th-century techniques of Johannes Gutenberg. Tours minuscule, the face he has just finished cutting "from scratch," is based on the lettering of Charlemagne's time.

Ken Hammel, acknowledged as a master by his peers, produces medical films for the Navy by day and spends evenings, weekends and holidays with a small hand press and a Chandler and Price power press in his Bethesda basement. "Printing has been a passion since I was ten," he says. But his real claim to fame. he insists, is the font of Binny and Ronaldson Roman No. 1 type he owns that dates from 1796. The matrices had been preserved "by a fluke," and he had the type cast from them about ten years ago. Other than that, he's mostly a basic Baskerville man.

When John Michael moved here nine years ago, his Acorn Press, which worked mainly with designers, architects, restaurants and art galleries, had been well known in Chicago for 20 years. He now keeps a Vandercook 1V and a Vandercook Universal 111 proof press, along with a 10 x 15 Heidelberg and three hundred cases of foundry type in his Rockville basement. Among other works, he did this year's Christmas cards for the Zoo, and prints special certificates for the National Park Service - hand set on handmate paper. "Letterpress has a tactile quality, an intimate appeal," he says. "Good letterpress printing digs into the paper and alters the face of a page. The light is reflected off the letters giving them another dimension. They're not just lying there like a glob of ink."

Roland Hoover, another pro, is Director of Publications at Brookings in real life, but at all other times can be found hovering over his two basement presses. He can have all the presses he wants, his wife has announced, as long as they don't take up any more space. He printed Linda Pastan's On the Way to the Zoo for Merrill Leffler's Dryad Press.

A Yale Engineering school graduate, Hoover says he's "developed a liking for precision machinery. I feel at home around that stuff. I'm also attracted by letters as abstract forms and in the use of language and the feeling of being in contact with an ancient and honorable tradition."

Mind, form and machine all come together over the basement press. "Words become incarnate," as he puts it, "stamped into old pine trees with lamp black."

It wasn't long after listening to Hoover carry on like that that Mark Carroll, chief of professional publications at the National Park Service, found himself the owner of a 1911 model Chandler and Price. (Hoover and a Brookings writer helped him haul it home.) The Pickwick Press makes modest forays into "bar mitzvah invitations and ephemera," its owner says.