THE GAMBIT is simple yet extraordinary: a superhero without a theme song.

Say Batman, Superman, Indiana Jones — the list goes on — and a theme clicks in. Hear a theme, and the mind plays the visual. Hans Zimmer and James Newton Howard have tossed that tradition out the window for “The Dark Knight”: Batman gets two notes. The Joker, only one.

It’s a radical concept for a film score, a technique more likely to be found in a Wagner opera. Those notes do not sit alone or on top of a brash comicbook score either. This is a score inspired by minimalism, repeated motifs that echo the work of Steve Reich’s “Music for 18 Musicians” and Philip Glass.

A Joker-like smile came over Zimmer’s face as he talked about his favorite aspects of the score, a feeling that he has achieved some sort of mischievous goal.

“It’s odd to put avant garde touches on a blockbuster,” he said. “It’s tremendously enjoyable in an obsessive way. Once we stepped away from supplying a hero’s theme, we spent most of our time getting rid of notes.”

ZIMMER, HOWARD and director Christopher Nolan worked together on the score for 2005’s “Batman Begins.” At that time, the idea of a jointly composed score by two of Hollywood’s most sought-after composers seemed like pure novelty. “Dark Knight” is hardly an encore — Zimmer and Howard gave Nolan an iPod filled with 10 hours of music cues based on just the script, which Zimmer contends the director memorized on flights to and from Hong Kong.

The score, which includes pieces composed prior to filming, has elements culled from Bach and hard rock in addition to the minimalists, and, listened to on its own, manages to get the heart palpitating.

The opening extends a full nine minutes and Zimmer swears it’s only two notes. “It was like an exercise. One tempo, two notes — what can you do with it?”

For the previous “Batman” film, Howard and Zimmer took a collaborative approach in which each would work on the same pieces to the point that today they can’t fully recall exactly who did what. The result, the composers agree, was that the “Batman Begins” score was textural.

“The Dark Knight,” in which the driving force behind the score was to heighten the sense of reality in the film, saw the work divvied between the two, with Howard given the task of creating musical portraits for the Joker and district attorney Harvey Dent.

Howard shaped Dent with elements of Americana, emphasizing brass on the high end and the low end. The Joker, he said, was the most fragile music in the score.

“The emotional extreme could not be much greater,” Howard said. “Hans called me and asked how we would show that morally he is completely corrupted. The idea was to use the brass. It seemed like a good way to go, but it’s so different from the rest of the movie. We took it and twisted it as the character loses ground. Harvey Dent is the emotional arc of the film.”

THE DARK KNIGHT” is filled with weighty issues — justice, power, corruption, anarchy and heroes — and the two composers sought to parallel its otherworldliness with sonic landscape of electronics and orchestra. Recording a perfect hit on a drum, for example, became a starting point for several moments in the highly percussive score. Nearly every note, Zimmer said, has been manipulated, from the corroding of piano sounds to the layering of horns.

“We come from rock ‘n’ roll and think in terms of record production, not just putting mics up,” Zimmer said, seated in the living room of his studio complex in Santa Monica, which is coincidentally designed in the red velvets and dark wood of Wayne manor.

The score was recorded at George Martin’s Air Studios in London, and Zimmer swears geography and architecture — brass sections were recorded in a church loft — play as big a role as the notes on the sheet music.

With the sound designers, Howard said of its uniqueness, “We created a world from the left corner of the screen to the right rear of the theater. Every movie you score you hope is unlike anything you have done before. You are always trying to not sound like yourself. The vocabulary for this score, we really sweated over. It sounds simple but there were hundreds of choices.”

Even though score-based soundtracks generally struggle in the marketplace, Warner Bros. Records is releasing the score album todayin four different configurations: a standard jewel case CD; a two-LP set; a special edition digipack and a collector’s edition with special artwork. The film opens Friday.