Michael Frayn's fascinating "Democracy" is a weird kind of love story -- the playwright's own, sort of. The object of his affection in this case isn't a woman, or even a man. It's a government.

Before your chin drops to your chest and your snores start to rattle the coffee cups, recall that Frayn was the writer responsible several years back for taking the rock-'em, sock-'em world of quantum theory and translating it into the elegant "Copenhagen." Frayn has a mind organized around the principle that college-level courses such as Particle Physics 101 and Introduction to Parliamentary Systems simply must have a theatrical life. And surprise of surprises: They do, thanks to the exhilarating verbs he finds for topics that strike the rest of us as the province of sedentary nouns.

The keys that make his plays so accessible are insight and warmth, and both are abundantly on display in "Democracy," which opened last night at the Brooks Atkinson Theatre. The play, a runaway critical success last year for the Royal National Theatre, retains its London director, Frayn's skilled longtime collaborator Michael Blakemore, but gets a new American cast, headed by James Naughton, Richard Thomas and Robert Prosky. The production is a step off the thrilling pace set by its London predecessor. Yet "Democracy" remains, for the moment, a one-of-a-kind Broadway experience, a play that actually deepens your understanding of the world.

It's smart, and despite its remoteness from the bread-and-butter domestic concerns of American voters, not at all condescending. "Democracy" is on one level the story of West Germany's struggle to establish a vibrant multiparty system. Of course, if that's all it was, it might just be for political science majors. (As it is, the first half-hour, detailing the rigors of coalition-building in 1960s Bonn, is more of a slog than you might wish.) But "Democracy" is also a moving account of the rise of an inspirational politician -- the magnetic chancellor of West Germany, Willy Brandt, who is portrayed by Naughton, a Tony winner for "City of Angels" and "Chicago."

What's more, it's a spy story, and as this aspect of the drama takes firmer and firmer hold, the evening becomes ever more engrossing. The intrigue is of the tabloid-sensation variety: It so happens that the fawning functionary who becomes Brandt's right-hand man is also an East German mole.

This in-house Judas, Gunter Guillaume, is our unlikely touchstone; it is through the eyes of the foreign agent, played with an invigorating charm by the eternally youthful Thomas, that we paradoxically get the most tender, emotionally layered portrait of Brandt and the challenge of navigating a country through the trenches of Cold War realpolitik.

Frayn intermingles the threads of "Democracy" the way a conductor ties together the sections of an orchestra. Though the play is largely structured chronologically -- beginning with Brandt's election as chancellor and ending with the fall of the Berlin Wall two decades later -- the characters talk across time and space. The device is used most frequently for Thomas's Guillaume, whose narration takes the form of secrets passed on to a Stasi contact, Arno Kretschmann, played here to engaging perfection by Michael Cumpsty.

And though Guillaume practices the most blatant deception in the play, it is one of Frayn's points that in a democracy, betrayals are as central to the process as alliances are. To wit, the members of Brandt's inner circle, like Helmut Schmidt (John Dossett), Hans-Dietrich Genscher (John Christopher Jones) and, most appealingly, the wily party leader Herbert Wehner (Prosky), are all schemers, stonewallers and backstabbers par excellence. The play constantly points out the characters' double loyalties: ministers who are ex-communists or former Nazis, lawmakers devoted to a region more than a country. Peter J. Davison's eye-catching bi-level set, its walls a honeycomb of mail slots, reflects the beehive mentality at the center of power; it's a manifestation of the futile attempt to impose order on political chaos.

While Brandt is on the stump with Guillaume in the hinterlands or off negotiating a treaty in Moscow, his brain trust -- an ironic term if there ever was one -- is endlessly posturing and conspiring; how does one govern in such a system, Frayn asks, when it depends on the alignment of the self-interest of so many players? The Stasi is, in fact, the least of Brandt's problems. Prosky's superb Wehner, avuncular and withering, is a master of situational ethics. He loves Brandt. At the moment. "We all know," he explains, "we can't get reelected without him."

The Brandt of "Democracy" is sly, too, of course, and he's blessed with the Kennedy touch -- "Camelot on the Rhine," they call his administration. It's clear that any actor playing a character with this kind of buildup has his work cut out for him. (Roger Allam, who was Brandt in London, brought an extraordinary soulfulness to the part.) Naughton has the voice of a pitchman and the bearing of a wealthy playboy (Brandt was a famed ladies' man), but as an actor he's a bit opaque. This trait worked for him more successfully in "Chicago" because as Billy Flynn, the media-darling defense attorney, he was sending up his own suave handsomeness.

His Brandt is sober, but also more spokesmodel than statesman; it's difficult to credit him as a historic figure given to both ecstatic moments of public triumph and dark bouts of self-doubt. It's by no means fatal to the production, though. Brandt is conjured so vividly in the accounts of those around him, Guillaume especially, that you imagine the man they're all discussing. (Even Mark Henderson's inspired lighting design illuminates Naughton as a man of dramatic gesture.)

Thomas's character, though, garners a larger share of your affection in this production, and this actually allows Guillaume to emerge as a more rounded figure, a man of complex motives. Though Thomas does not match the physical description as Frayn relates it -- he is not the greasy "meatball" the script refers to -- he does live up to the more difficult task Guillaume presents, making plausible the notion that a man can be servant to both sides in a war and still seem honorable.

As a microscope on the ineffable qualities that define great leaders, "Democracy" is an occasion for some wistfulness. Watching Brandt in private, funny moments as well as those of remarkable brinkmanship, you wonder: Whatever happened to officeholders who both played and transcended politics, cultured individuals who could communicate the idea that they embraced the whole of humanity? "Democracy" leaves you with a powerful taste of what the world needs now.

Democracy, by Michael Frayn. Directed by Michael Blakemore. Costumes, Sue Wilmington; lighting, Mark Henderson; sound, Neil Alexander. With Julian Gamble, Terry Beaver, Richard Masur, Lee Wilkof. Approximately 2 hours 30 minutes. At Brooks Atkinson Theatre, 256 W. 47th St., New York. Call 800-755-4000.

Richard Thomas and Michael Cumpsty as a mole in the West German government and his East German handler in Michael Frayn's "Democracy."Richard Thomas and James Naughton as Gunter Guillaume and Willy Brandt in "Democracy."