"We only rehearsed one encore!" insisted Ron Moody, stepping momentarily out of the role of Sir Joseph Porter, K.C.B (First Lord of the Admiralty), and directly addressing the "HMS Pinafore" audience in the Kennedy Center Opera House. But his pleas were unavailing; the audience kept up its insane rhythmic clapping, insisting on more details about how he became "the Ruler of the Queen's Na-vee."

"We only rehearsed one encore!" he repeated, and was drowned out by more applause. After several more tries in English, he went on to French, German and Italian -- then, before giving up, he asked the audience desperately, "What language do you speak?" Finally, he began to improvise encores: "Jack and Jill went up the hill; as far as I know, they're up there still," he sang to the familiar tune of "When I Was a Lad." And the audience applauded again, willing to give him an "A" for effort.

The "HMS Pinafore" that will spend the next six weeks in the Opera House (coexisting with a fine "Ruddigore" next door in the Eisenhower) is directed by Brian Macdonald, whose "Mikado" is still fondly remembered from a few years ago. Like that earlier Canadian import, it is intensely choreographed, vividly staged, salted with topical humor and imbued with a zany energy that never (What, never? Well, hardly ever) lets up. Being directed by a choreographer, this company dances its curtain calls while the band (conducted by Berthold Carriere in a British sailor's uniform) plays on. Last night's audience kept them dancing until they were ready to drop.

The topical humor added to the script last night was a bit less prominent and less barbed than the inserted lines remembered from "The Mikado," but the audience loved it when Moody sang that to get a political appointment "the way to start/ Is to take a course in politics with Gary Hart." Hart can be trusted to keep his word, he explained, because nobody will take it.

Finally, searching desperately for another encore, he advised the audience to cultivate "an actor's grin,/ And you can get an office down in Washingtin." That's not a misspelling; it's his pronunciation. And the crowd went crazy anyway. "How kind," he remarked graciously after tumultuous applause provoked his first encore, but the applause for that number could have been based on political blood-lust rather than kindness. At the final curtain, though, it was sheer enthusiasm.

The singing in this production is, on the whole, less opulent than in the Washington Opera's "Ruddigore." But the singing is easily up to the standards (a bit below opera, a bit above Broadway) set by the D'Oyly Carte Company, late, lamented keeper of the sacred flame.

Meg Bussert, in the role of the captain's daughter Josephine, sang well but eclipsed her singing with comic acting in a very special, rarefied, mock-Victorian style. She posed, she languished, she wept prettily and she had attacks of the vapors. Whenever she came onstage, there was a flower in her left hand that she would fling, moments later, into the audience. Arlene Meadows (Little Buttercup) contrasted with a warm, rich mezzo voice, a rose-colored personality, a plump and pleasing stage presence.

Moody's virtuoso performance as Sir Joseph tended to overwhelm his less colorful male colleagues, except for Ted Pearson, a splendidly unsavory Dick Deadeye, who added a bit of scene-stealing to his other crimes. But Michael Brian was a stalwart Ralph Rackstraw, vocally and theatrically; David Dunbar, despite a few moments of vocal insecurity, gave a good account of Captain Corcoran and Paul Massel and Stephen Beamish stood out in supporting roles.

A significant attraction of this production is Susan Benson's designs. The entire show takes place on the deck of the Pinafore, which is never seen in perspective, only in detail -- a mast here, a crow's nest there, hammocks in which the crewmen sleep like the victims in "Coma" when the curtain goes up, a spider's web of rigging on which they swing as they sing their welcome to Sir Joseph, and a giant Union Jack, which sometimes serves as a backdrop and sometimes becomes actively involved in the choreography.

Some touches (such as the strobe lighting at the beginning of Act 2) may disturb traditionalists -- a strong contingent among the admirers of this repertoire. But for most members of the audience this production's brightness and vitality are their own best defense. It looks like a lively six weeks coming up in the Opera House. But they'd better work up some more topical encores for Ron Moody.