"The Royal Hunt of the Sun," Peter Shaffer's 1964 epic about the conquest of Peru, finds the Washington Shakespeare Company in vintage form. The play is wildly ambitious, the direction is bold, the acting is spotty, and on opening night the air conditioning went out in the Clark Street Playhouse.

Apparently the WSC won't have this spacious, unrefined warehouse to kick around in much longer, and for all the building's flaws, a leaky roof among them, it will be missed. (The property is slated for private development in the near future.) Shaffer's vision is Shakespearean in pitch and scale, with Spanish conquistadors and Inca warriors squaring off in a play that shakes its fist at God, and the pleasure of Clark Street has always been how easily this sort of thing fits in the high-ceilinged industrial space. It's an effect you can't get in a converted storefront or church basement, or even on a gorgeous, well-equipped but comparatively small (and comparatively inflexible) stage like the Metheny at the Studio Theatre.

Director Steven Scott Mazzola works the warehouse beautifully in this production. It's a bare-bones affair, to be sure, and for a play that ought to glitter with splendor and rumble with conquest, it looks a little chintzy. The ivory linen trousers and leather armor of Cynthia Abel Thom's costume design and the scrolling vertical tapestry at the back of set designer Matthew Soule's generally open stage are fine as far as they go, but there's no escaping the sense that this is epic on the cheap.

Still, Mazzola adroitly seizes each opportunity for pomp and pageantry, and the bigger the scenes, the better the staging. Incan king Atahualpa makes his entrance borne aloft by bare-chested warriors; Spanish conquistador Francisco Pizarro leads his band of men over the Andes, with actors leapfrogging as if scaling high rocks and squeezing sideways as if through tight crevasses; the slaughter of the Incas -- who vastly outnumbered the Spanish, yet didn't resist -- is rendered with a flurry of clear action and drums pounding from every corner of the space. The original music by Mariano Vales, rich with mournful Peruvian flavor and sometimes sung by three women who form a kind of wandering chorus, adds to the sense of cinematic sweep.

The way Shaffer operates, the spectacle and grandeur set up a comparably large intellectual inquiry. (This, of course, is the man who later penned the stately primal screams "Equus" and "Amadeus.") Most simply, Pizarro's dilemma comes from slaughtering Atahualpa's men and then imprudently promising to set the aggrieved leader free -- a promise he might prefer not to keep.

But conscience, religion and even political systems are all under scrutiny here. Pizarro claims Peru's dazzling riches for Spain and spearheads the advance of Christianity, but Shaffer imagines a conquistador who begins to question his own claims of moral superiority once he observes the Incas' peaceable agrarian society and enlightened sun king. (The implication of this production seems to be that modern conquerors should be so reflective.)

The WSC has evolved over the years from an actors' company to a director-driven troupe; the warehouse clearly inspires directors' imaginations, but the WSC has had increasing difficulty finding and keeping performers who can command the space. With its inflated language and lofty themes, "Royal Hunt" cries out for a particularly majestic presence in the role of Pizarro, and James Foster Jr. doesn't quite deliver. Vanity, world-weariness and anguished soul-searching obviously are his goals, but Foster tends to flatten everything into an extended sneer. The vacuum this leaves at the center of the show is considerable.

The rest of the sizable cast is up and down, with the most positive impressions coming from Peter Pereyra (who gently renders Atahualpa as openhearted yet determined) and Daniel Ladmirault (who takes the role of the fervently righteous chaplain and plays it to the hilt). The show may be a textbook case of overreaching, but it's hardly a foolish or embarrassing stretch. Under Mazzola's guidance the quest is always noble, and glory is nearly in sight.

The Royal Hunt of the Sun, by Peter Shaffer. Directed by Steven Scott Mazzola. Music director, Mariano Vales; choreography, Krissie Marty; fight choreography, John Gurski; lighting design, Ayun Fedorcha; sound design, Matthew Nielson; props, Eleanor Gomberg. With William Aitken, Leslie Sarah Cohen, Brian Crane, Edward Daniels, Chris Galindo, Theo Hadjimichael, Katherine E. Hill, Jim Jorgensen, Steve Lee, Matt Mezzacappa, Alex Perez, Francisco Reinoso, Beth Madeline Rubens, Nick Scott, Michael Sherman, Addison Switzer and Shane Wallis. Through Aug. 28 at the Clark Street Playhouse, 601 S. Clark St., Arlington. Call 800-494-8497 or visit www.washingtonshakespeare.org.

The cast invokes the slaughter of the Incas by the Spanish conquistadors in the ambitious yet uneven production by the Washington Shakespeare Company.