As a name for a dance troupe, "Harry" makes you stop and think. Is it a masculine nickname, or, as some have suggested, a verb? The dancing by the group that bears this appellation also makes you think, but it doesn't often stop. The choreography by Senta Driver, who founded "Harry" in 1975 and is one of its four performing members as well, has a dogged propulsion about it that dries onward through a heroic, often ruthless expenditure of energy.

And though Driver's work provokes though, it is anything but cerebral. Her movement idiom keeps one in constant awareness of the body -- its bone musculature and bulk; the tensions that hold it together and those that spur it to action. Feet stomp, limbs flail and thrust, trunks twist and wobble, plunge and roll, and always with the sense of forces in contention, internal and external.

Driver's pieces, moreover, seem blunt and businesslike, yet each one is edged with lacerating wit.

"Harry" presented the first of two programs at the Washington Project for the Arts last night, as part of its two-week area residency under WPA auspices involving workshops, classes and lectures as well as performances. In all three works of the evening, two of them new to Washington, ambiguity was a leitmotif. The title, "Primer," for example, suggests a brief and easy introduction to basics, but the piece is more like an exhaustive and exhausting encyclopedia of movement possibilities, from syncopated marching to headstands.

"On Doing," in fact, turned out to be a tongue-in-cheek "illustrated lecture" on ambiguity in dance performance. As soprano Margaret Goodman recited and sang Tom Johnson's droll verbal and musical conundrums about "doing it," "really doing it," "hardly doing it," "overdoing it," and so forth, the dancers gave a fixed circular routine the aptly corresponding inflections of meaning.

No less paradoxical is "Sudden Death," in which the breakneck, parallel struggles of a couple (for a tie-breaking point, one presumes) end abruptly when the woman grabs the man for a prolonged, open-mouthed kiss. Is the kiss an act of submission? Or aggression? Or the triumph of passion over competition? The choice is the viewer's.

It's no great surprise to discover that Driver earned a degree in Latin and philosophy. Her work has a metaphysician's obsession with essences, and a philologist's hair-plitting rigor. Yet her choreography is as full of invention as it is of riddles. There's a pugnacious, almost punishing quality about her kind of dancing that can be off-putting, as can its extremes of proportion. Yet in an era so devoted to accessibility, froth and soft nostalgia, it's refreshing to encounter Driver's challenging creations, at once amusing and severe. Driver makes audiences work as hard as she and her dancers do.