WHAT MAKES a book?

Is it the stack of pages (often called leaves and appropriately manufactured from the pulped wood of trees)? Is it the leather or cardboard spine that forms its backbone? The stitched or glued binding that holds it together (but inevitably falls apart)?

Does its very ephemerality make it more precious or merely more disposable?

Does a book consist of the text and/or pictures that often -- but not always -- fill it, or is it equally the blank space between its words, the whiteness of its margins and gutter, the invisible ideas it holds?

Does its paradoxical nature lie more in its portability, its hermetic self-containment or in the tendency of its contents to spill out, contaminating -- but just as often purifying -- the universe?

"Book as Art XI," the National Museum of Women in the Arts' 11th annual exhibition of artists' books, does not pretend to answer any of these questions.

Frankly, it doesn't even ask them, at least not intentionally, but these issues percolate up through the porous ground of this richly rewarding show anyway, along with many other questions and notions raised by the 50-odd (and I do mean idiosyncratic) works that curator Krystyna Wasserman, director of NMWA's Library and Research Center, has assembled.

Some of the art works here are cousins to what you would think of as traditional published volumes. I'm thinking of works like Zimbabwe-born Katie Alfonso's "African Wildlife for Children," one of three abecedarian primers in the show, along with Susan Rotolo's alphabetical listing of Italian foodstuffs and Pamela Zwehl-Burke's roster of words describing her emotions after divorce.

They are pieces that can be opened and closed, pages can be turned, text that can be "read" in the literal sense of the word -- although all of them remain tantalizingly out of reach under glass vitrines or guarded by signs that say, "PLEASE DO NOT TOUCH." (That's the one thing missing from this otherwise satisfying show: feeling the heft or delicacy of a book in your hand.)

Others are not really books at all, at least not in the strictest sense of an artist's book -- a unique or limited-run volume of some sort, typically handmade. Molly Van Nice's "Notings of the Journeyman" series, for example, is closer to sculpture. Ten works from the conceptual artist's 15-part installation are displayed here, most of them consisting of hinged specimen boxes filled with such miscellany as animal skulls, apothecary vials, seed pods and passports. Although they open and close like books and are lined with minutely beautiful but illegible handwriting, Van Nice's portable archives are more box than book. Still, they form a fantastically detailed travelogue -- each one accompanied by a letter to a fictional "Mondo Poltroon" written during an imaginary journey to a nonexistent place.

Even Van Nice's "Notings of the Journeyman X, Dining Out," which does incorporate actual books, presents them pierced by hunting arrows, charred on the end of a barbecue skewer and served like a sandwich on a plate, complete with a fake slice of Swiss cheese between the covers. It's more commentary on the nature of the book than book itself.

But that's okay, because where "Book as Art XI" is at its most intriguing is where it is least "bookish," if you will, where its offerings get over trying to look like their stodgily literate neighbors (the show is mounted near the stacks of the museum's library). The best of "Book as Art XI" maintain only the most tenuous hold to the publishing world.

The ideal representation of this freedom is Dianne L. Reeves's organic "Depth of Rage," a fetishistic hybrid whose spine is quite literally made of fishbone. Its pages -- handmade paper rudely fashioned from wood and jute -- resemble bark or dead leaves. A tree root appears to grow from one end and then morph into a pair of antlers. This so-called "book-object" (according to Wasserman's wall label) speaks eloquently to our fears and dark emotions without using any text or imagery at all -- save for those that come unbidden from the viewer's subconscious.

Other strong entries include Nan Haid's wry and strangely moving "Nanoseconds 2," a visual diary of sorts in the shape of a patchwork coat. In 352 panels, culled from ticket stubs and the comics page and the detritus of daily life cut and sewn together to form a map-lined garment, Haid records the mundane stings and triumphs -- both tiny and large -- of a single year in her life, 1994. Such terse, stamped legends as "Bad Cold," "Amy's Pregnant" and "Pesto" may not be the stuff of high drama, but their cumulative effect is surprisingly moving.

Miriam Beerman's approach to book-making is not to make but rather unmake, as she takes a black-and-white catalogue from some unnamed art exhibition and defaces it with her own automatic ink drawings and arbitrary transcriptions of poems by Rainer Maria Rilke. By destroying what previously existed in an act that many would consider an act of literary vandalism, Beerman creates something totally original.

That paradoxical notion of the printed page as potential blank slate is echoed in "Palimpsest: Erasure and Recovery" by the artists' collective know as WAVE. These six Texas artists, who define "book" as merely a loose stack of tablets printed in an edition of 15, have created a series of images -- in silk-screen, block-printing, metal leaf, photography and drawing -- each of which deals with the idea of the removal and reconfiguration of that most sacrosanct thing: the original text.

Becky Hunt's two contributions also illustrate these opposing poles of book fabrication -- construction and deconstruction. The neatly-hinged triangular panels of "Everything Has Its Own Vortex" unfold to form an intricate, helix-shaped book when open, imprinted with a single line from a William Blake poem. "The Further Poetics of Space," however, takes random phrases by writer Gaston Bachelard and prints them on scraps of rice paper heaped in a black box.

Each one must be read -- or like Van Nice's "Dining Out," digested -- in utterly different ways.

So what is a book? Artist Natalie D'Arbeloff, whose "Pater Noster" contains the Lord's Prayer in the terraced shape of a ziggurat, nicely defines the undefinable beast when she calls it, "a surprise package one opens with anticipation and whose contents are revealed little by little."

That tension between opacity and wide-openness is, as any bibliophile knows, the joy and frustration of any book, which only ever discloses its secrets over time and with a certain concerted effort from the reader.

BOOK AS ART XI -- Through Dec. 31 at the National Museum of Women in the Arts, 1250 New York Ave. NW (Metro: Metro Center). 202/783-5000. Open 10 to 5 Mondays through Saturdays; Sundays noon to 5. Admission is by suggested donation of $3; $2 for students and seniors. Web site: www.nmwa.org.

Public programs associated with the exhibition include:

Sunday from noon to 2 - "Beyond the Book." Children ages 9 to 12 will tour the exhibition and create their own travel journals. Call 202/783-7370.