BERKELEY, California--Radiohead is not for the faint of sonic intellect.

The UK pop art rockers serve up rock and roll in its most dense, demanding and, at times, indigestible form. In doing so, they require what few rock bands even ask of their audience: full attention.

But under a haunting layer of fog Friday night at the Greek Theatre in Berkeley, California, the audience responded in spades.

The crowd stayed in rapt silence for almost all of the new songs the band unveiled in the nearly two-hour set, and erupted into cheers in approval when they concluded. It's quite a sight to behold, this mass of young people packed like sardines into an amphitheater for a rock-and-roll concert, remaining patiently stoic while the music is being played as if they were at an opera or the symphony.

Radiohead is in the midst of a brief US tour to test out a new batch of songs that will appear on an as-yet-untitled album on an as-yet-unnamed label (if any). Friday night's set consisted of almost a dozen new songs and a handful of old ones, and several of them saw the band step out of its usual opaque, abstract sound and opt for music that was simpler, more straightforward and, dare we say, even funkier.

But even at its funkiest, like on the new, decidedly percussive track "Down is the New Up," which featured frontman Thom Yorke engaging in some beatboxing and some Prince-like vocals, the Radiohead trademarks remained.

Every time the percussion--both guitarist Johnny Greenwood and Ed O'Brien joined drummer Phil Selway by playing mini-drum kits--began to provoke the crowd into clapping or waving their hands as if they just didn't care, Greenwood would throttle a few off-kilter guitar chords, threatening to pull the rhythm apart but instead painting an entirely new aural landscape.

Although some of the new material opts for a simpler sound, as on the bass-driven groove of "15 Step," Yorke displayed another of Radiohead's trademarks: his use of literary lyrics that are both cryptic and expressive. The lyrics to "15 Step" could almost serve as a summary of the Radiohead sound: "How come I end up where I started/How come I don't end where I belong/Don't take your eyes off the ball again/You reel me out then you cut the string."

"15 Step" also showed off Yorke's voice, which can be downright gripping. As the Radiohead sound has evolved over the years from straight rock to a musical form of abstract expressionism, so have Yorke's vocals. He sings as though his voice were an instrument, often trailing off into wordless verses that take on the characteristics of instruments that aren't onstage.

The concert wasn't all test-tube fare. Over the minimal electronica of the environmentally concerned "Idioteque," off 2000's Kid A, Yorke conveyed a sense of urgency without being shrill. Another Kid A track, the pulsating "Everything in its Right Place," the closest thing the band's had to a hit in the past six years, closed the show's second encore and left the crowd buzzing.

Sound troubles seemed to plague the band at times, no more apparent than when Yorke had a hissy fit at the outset of "Idioteque," gesturing dramatically toward the sound board and his microphone.

Although the band is playing smaller venues than usual for this listening party-style tour, it hasn't skimped on the extracurriculars. Ten rhomboid-shaped screens behind the band showed clips of band members at odd angles, giving the crowd up-close views of places like Yorke's chin, Selway's forehead, or the neck of Greenwood's guitar.

Greenwood was the revelation on this night. Although he's known as the coleader with Yorke, the diminutive singer is clearly the face of the band, particularly as he steps out this month with his first solo effort, The Eraser.

But while Yorke's versatility was on display as he changed instruments with every song, Greenwood did so often on the same song, bouncing from keys to guitar to his Kaoss pad, which allowed him and O'Brien to loop live samples of Yorke's piano and singing.

He did that on "Videotape," perhaps the most compelling of all of the new material. Yorke opened the song with the line: "When I'm at the pearly gates/this'll be on my videotape," and before long he started into piano chords while Greenwood played a backward-processed guitar. The song surges several times, darting off each time you thought you had a handle on it, before building into full-fledged garage rock.

That's the Radiohead moment: The songs dig their way into your head until you're bobbing to them, and then they quickly shift gears. If you have the musical acuity to keep up--and Radiohead's legions of fans certainly seem to--it can be quite a ride.