DON'T TAKE too literally the title of the exhibition "Sculpture in Four Dimensions" at the Art Museum of the Americas. In the words of Sculpture magazine Managing Editor Twylene Moyer, who organized the juried show with museum director Ana Maria Escallon from submissions that were both international and local (more on this later): "Don't expect any concrete representations of the hypercube's abstract geometry here." In other words, even though some works incorporate such airy-fairy media as "time" (one of the ingredients in David Meyer's "False Theory"), this is a show in which the definition of the titular dimension falls closer to something like "poetry" or "unexpected possibilities" than anything that can be measured with a yardstick, albeit a theoretical one.

What this also means, in practical terms, is that the most successful pieces, at least in terms of hewing to the theme, are those that are the most difficult to see.

I'll start with one example, which a casual visitor might easily overlook, if for no other reason than the fact that it's unlabeled. In fact, if you walk outside the museum to get to the garden behind it, where several of the sculptures have been installed, there's a good chance you'll find yourself standing on this particular artwork. There is no sign -- at the request of sculptor Carolina Mayorga of Colombia, I'm told -- because the artist didn't feel her piece was successful.

She's wrong.

Called "Grass Clock" and consisting of words "written" in brown sod that the artist had previously covered up next to the museum's outdoor pool, the simple work is as conceptual as it is sculptural. On the afternoon I visited, just before the opening reception, this message in patches of dried grass was faint but discernable: "As this sculpture fades, 22,500 children will die in war." By the time you see it, more of the once-green ground cover will assuredly have filled in, making it even harder to read, just as Mayorga's prophecy will have assuredly drawn closer to its sad fulfillment.

Other works vie with Mayorga's in subtlety, if not political punch, among them Katherine Kavanaugh's "Air," a gorgeous, site-specific installation -- no, make that flock -- of sewing needles stuck into the wall near the second-floor bathroom. Along with Margaret Boozer, Lynden Cline, Chas Colburn, Carolyn Jean, Erin Root and others, Kavanaugh is one of several fine Washington area sculptors whose works are showcased here. The show itself is one of several in an ongoing celebration of the 20th anniversary of the Washington Sculptors Group, who in this case have been paired with artists from the Americas (e.g., Argentina, Chile, Peru). I particularly liked Boozer's "Cross Eye Bird," a composition whose central, unearthed root, framed by an old wagon wheel, is a Duchampian departure from her more familiar ceramic art.

Intriguingly, the women outnumber the men here more than 3 to 1.

Could this perhaps account for that certain -- oh, I don't know -- delicacy alluded to earlier? It's probably sexist to even suggest that, yet it's easy for the thought to cross one's mind when encountering works incorporating feathers, hanging rayon paper, flour (and flowers), lipstick, optical fiber, porcelain, velvet, salt and dead bugs embedded in sheets of resin. To be sure, some of these materials appear in pieces by men, and there are certainly women in the show who work with steel -- as well as other, more "rugged" material.

Gender aside, though, the truest reason for this daintiness is the show's theme, which emphasizes ineffable qualities that go beyond length, width and height. As is often the case, the more unorthodox the material -- or, more specifically, the more fragile and ephemeral a work is -- the more it draws our attention away from what it's made of to the immaterial. Sharyn O'Mara's "Untitled: corner 1," a gossamer-like cloud of shimmering optical fiber and monofilament that suggest a beatific visitation, is such a piece. So is Lucy Norman Spencer's "Her Jewels," a sweet little nest of burnt wood containing egglike balls of Kosher salt and paraffin wax.

In a town known for its earthbound sculpture gardens, memorials, monuments and equestrian statuary, "Sculpture in Four Dimensions" is a welcome respite. The airiness and ethereality of its art do not, for the most part, connote a lack of gravity. Yes, there are some clunkers in this jewelry box of a show, but there also are some real gems.

SCULPTURE IN FOUR DIMENSIONS -- Through Sept. 30. Art Museum of the Americas, 201 18th St. NW (Metro: Farragut West). 202-458-6016. Open Tuesday-Sunday 10 to 5. Free.

Above, Lucy Norman Spencer's "Her Jewels," a nest of burnt wood with egglike balls of Kosher salt and paraffin wax. At left, Sharyn O'Mara's "Untitled: corner 1" glows with optical fiber and monofilament.Lika Mutal's "Stone Tide" is travertine with algae calcareous.