With a little help from Washington's corporate base, the city's artists are at last beginning to get commissions to make major works of art for public spaces here - the kind of career-expanding projects no artist can undertake alone. With luck, they will inspire others.

Two recent examples feature prominently on the gallery scene this week. Pyramid Gallery is showing studies for Gay Glading's fabulous space-unifying banners commissioned by the White Flint Shopping Center, along with a slide show outlining how the gigantic project was carried out.

And out on the plaza in front of a new office building at 1220 19th St. NW is Ed McGowin's first monumental steel sculpture, placed earlier this week. He is having a related show at Fendrick.

McGowin's 12-foot high sculpture is a handsomely shaped eccentric hexagonal box made of Cor-ten steel, with four Plexiglas-covered windows slit in at the corners. Irresistibly lured to look inside, the viewer is confronted with a strange tableau - a white-painted interior filled with a system of rusted old gears, pulleys and winches form which cables extend and are attached to the walls.

There is no way for the viewer to get inside, but if the machinery did get started, it would serve to collapse the whole sculpture from the inside. As yet incomplete, the interior will, according to McGowin, eventually hold a dirty old ash tray and other evidence of former occupancy. There also will be a blue noon sign that says "Do Not Touch."

McGowin got the idea for this work when he looked at the King Tut show and saw in the pyramids "a monumental form on the outside combined with the excitement of what was going on the inside.

"This concept for me is a very big one," says, "because it is a way of dealing with large outdoor works without having to give up the interior tableux, and the more intimate, personal and narrative work I like to do."

The project was funded by an $8,000-grant from the National Endowment for the Arts, made through the Philips Gallery, was awarded to match the $8,000 from JBG Associates, real estate developers who own the building in front which the sculpture stands.The grant was made through NEA's "Art in Public Places" program.

McGowin's show at Frendrick includes several large airbrush paintings, all proposals for objects that could go inside future monumental sculptures. These include a bronzed birthday cake and a wrapped gift enclosed in a sealed Plexiglas box, a permanent enigma and a metaphor for a proposal for another very large and impressive sculpture-with-interior, somewhat more refined and elegant than the pioneer work on 19th Street. With luck, it, too, will be built.

Also featured at Pyramid, along with Gay Glading's White Flint Project, is Manon Cleary's White Rat Project, a series of oils starring one or more white rats which the artist kepts as pets and has obviously come to love. One rat portrait, a particularly loveable one, Cleary goes so far as to call "Self-Portrait."

More important than the subject matter, which you either love or hate, is the new adventurousness evident in the most recent compositions, where rats are menacingly posed with single figures in ambigious scale and space relationships. Though borrowed largely from surrealism, these devices add interest and complexity to the growing painterly skills of this gifted artist.

Speaking of painting, don't miss Jerry Clapsaddle's paintings at Max Protetch. Clapsaddle is the best new painter to turn up on P Street NW in a long time. Now teaching at the University of Maryland, the artist was previously an assitant professor of art at State University of New York, Oneonta. Though this is his debut here, he has a long list of shows to his credit.

Working on a grid format in a totally obstract mode, Clapsaddle makes luscious paintings which recall, but in terms of meaningful expression, surpass, the work of David Headley.

Though her paintings are well-known and much loved by visitors to the Philips Gallery here, of which she was co-founder, artist Marjorie Philips has never had a solo show in a commercial gallery here before the current one at Bader. Here is revealed not only the broad range of her interests - from a pot of delicate geraniums to a night baseball game at JFK Stadium - but the broad range of her talent as well.

In recent years the still lifes have been stronger, surer, made with more expressionistic brushstroking. But that boldness was already evident in several large landscape compositions form 1958-59, such as "Town and Mountains," not widely shown before. It is in these large works where Philips' real powers and range as both painter and poet are fully revealed.

Ben Mahnoud, a West Virginian now living and teaching outside Chicago, is showing at the Wolfe Street Gallery in Georgetown. Mohmoud paints with his right hand and draws with his left, and frankly, I like his left hand better.

The several pencil drawings on view reveal an extraordinary draftsman who combines bits of photographic reality into unlikely, enigmatic situations, and then distorts the whole image, as if seen through a distorted lens, which it was not.