Washington is in the middle of a sculpture explosion.

Following a summer dominated by big sculptural events - the arrival of the Henry Moore in front of National Gallery East, the Di Suvero in front of the Hirshhorn (just painted a pointless blue and white) and the gurgling smoke-belching fiasco called "Centerbeam" alongside the Air and Space Museum - there now suddenly seem to be sculptures, good and bad, strewn all over the public spaces of this city.

And the pace quickens as sculpture exhibitions by Washington artists proliferate, inside and out, from the Corcoran's current Area Sculpture Show to "Outdoor Sculpture, 1978," 23 large works by 15 area artists now winding down to a Wednesday closing after a summer sprawling on the grounds of Northern Virginia Community College in Annandale. There suddenly seem to be Washington sculptors - as well as those sculptures - all over the city.

But nowhere is the presence of sculpture, famous or new, more surprising than in the commercial galleries here. Only two years ago most Washington dealers stayed away from sculpture of any real size. "You'll never sell it," they told Diane Brown, then a fledgling dealer on P Street. She's been selling it like hoecakes ever since, and so have several others.

In a complete flip-flop from the '60s when commercial galleries set the pace and the others followed, the galleries have now caught up with a trend seemingly brought about by large infusions of cash from an unwitting trend-setter, and the biggest sculpture patron of modern times - old Uncle Sam himself. It takes money to make sculpture, lots of it. For the first time in years, public corporate and now private patrons seem to be ready and willing.

Which is all by way of saying that the current sculpture shows around town are numerous, and a few of the best are noted here.

John McCarty, who has justifiably taken a prize at the current Corcoran Area Sculpture Show, is exhibiting new assemblages in steel at Diane Brown, 2028 P St. NW. Here, as in last year's maiden show, also at Brown, McCarty's extraordinary gift for the expressive, mood-porvoking abstract sculptural form is revealed.

The current constructions, however, are more ambitous, and more vertical, often based on a "gate" motif which somehow manages to conjure a mood both Japanese and African. McCarty seems to have no trouble at all expressing himself in both large and small-scale pieces. Brown's faith was well-placed. Through Nov. 11.

The new Wade Gallery at 1726 21st St. NW, two blocks past the Phillips Collection, continues to move strongly ahead with a show of sculpture/constructions by Bill Alpert, a New York artist who starred in Wade's opening group show last summer.

If there were any reservations then, there can be none now. Alpert is a prolific virtuoso of both color and form, and with astounding gusto he seems to be able to transform and reassemble any old crate, or shower curtain or cardboard box into art, or at least into something well worth looking at.

And his range is wide, from several huge, brash, wall-filling works like "Nobody Knows the Colors I've Seen" to the delicate and lusciously colored "Simple Piece" and "Begonia" hanging quietly upstairs. Alper's work is upbeat and fun, and his vitality infectious.Through Nov. 4.

At Gallery K, 2032 P St. NW, Paris-trained Japanese sculptor Yoshihiko Taniguchi is showing a series of immaculately executed cubes and rectangles of wood, marble and metal, wherein he explores the largerly hypothetical question of how they would look if they were just beginning to melt. Combining a California-like imagination with exquisite Japanese craftsmanship (which is the end prevails), these sensuous forms provide greatest pleaure when Taniguchi keeps it simple. He goes completely amok when he combines wood and metal into flashy, pretentious ensembles. "Squeezed Form" is the sole exception. Closes today.

Others of note, but not reviewed: Dickson Carroll's fantasy mobiles and stabiles at Gallery 4, 115 South Columbus St., Alexandria; and Martha Jackson's ceramic sculptures at Gallery 10, 1519 Connecticut Ave. NW. Sculpture by William Calfee go on view at the National Academy of Sciences on Nov. 6.

Washington has another strong suit at the moment in the proliferation of good realist painters, and the newest talent to turn up is a young woman named Michal Hunter, now showing at Fraser's Stable Gallery, rear of 1910 S St., NW.

For now, Hunter is preoccupied with making portraits, commissioned when possible, just for fun otherwise. And they are fun. Both a photographer and a painter, Hunter works from her own upheat black and white snapshots to establish format and attitude. In the paintings friends smile casually and a bit self-consciously, as one does at a camera, while holding dogs in check or showing off a plant. Sometimes Hunter uses herself as subject, usually at play, or sunbathing on a roof. She and her friends seem to have a superabundance of the sunny, happy good times that snapshots used to recall.

Despite the photographic base, however, there are ultimately paintings, enhanced in the transition to paint by taking advantage of the added possibilities. The full-length, frontal figures take on new pictorial life by fairly bursting out of the edges of the canvas. The seductive textures are rendered with great skill and effect. Overall, these are living, breathing presences.

This is particularly true in the more formal commissioned portraits which incorporate specific autobiographical information. "Peter," for example, is here shown in a bold and telling pose, sitting on his motorcycle even while in his own rather elegantly appointed front hall. He is obviously more attached to his bike than to anything else. "Richard" fairly reeks of the urbane, grandee art collector.

Another portrait of curator Walter Hopps paying a nighttime visit to a coffee shop counter is a classic study of Hoops - the cigarette stub, double-breasted corduroy jacket and confronting visage unmistakable, and all wrapped, in California orange neon. This and more through Nov. 4.

Michal Hunter, incidentally, is also included in another show called "Towards a New Portraiture" now at Government Services Savings & Loan, at 7200 Wisconsin AVe., Bethesda. Here other works by Manon Cleary, Joe White and John Winslow suggest that what is implicit in Michal Hunter's work is, in fact, present in the work of other Washington artists as they pursue their increasingly interesting search for a new kind of painted portraiture. Through Dec. 11.

Christopher Muhlert, also formerly of Washington and now of Iowa City, has just opened an uneven show of abstract paintings at Barbara Fiedler Gallery, 1621 21st St. NW., in front of which a Yuri Schwebler sculpture has been installed. Since 1971, Muhlert has been working in a large, circular format, in which short ribbon-like twists of color snake their way around and into a background that recalls almost verbatim the paintings of Clyfford Still.

In the most complex piece, striped ribbons invade green space and succeed in creating a feeling of almost frenzied activity. Less successful, however, are works like "Medusa" and "Aditi" which are flaccid in both form and color. Best by far, in this view, is the entirely different "Yellow Amber," from a spiral series. The drawings are also relatively strong, despite their name-dropping titles. Through Nov. 17.

Juan Downey, formerly of Washington and currently artist in residence at New York's Channel 13 TV Lab, will be at Fonda del Sol (2112 R St. NW) tonight from 7 to 9 p.m. to open a show of new videotapes, drawings and paintings, and to talk about his recent filming among the Yanimami Indians of the Amazon basin.

Surely one of the more gifted video artists currently at work, Downey's video piece "Last Meninas" was a standout in the Whitney's recent "Art About Art" show. This exhibition, Downey's first Washington solo in a decade, will continue through Nov. 18, after which it will proceed to the Musee de l'Homme in Paris. Hours are off-beat at Fonda del Sol: Tuesdays through Saturdays, noon to 2 p.m. and 4 to 7 p.m.