BERKELEY, Calif. — With punk-rockers Sleater-Kinney standing on a huge, open stage in the late-day sun and Sonic Youth filling the headlining spot with long, spooky jams, the all-day festival at the Greek Theater here Friday was anything but your typical rock festival.

Which is perhaps why this gathering of indie and indie-bred rock bands was called This Is Not a Festival.

"I'll admit I was skeptical," a tired but elated Maggie Yates, 29, of Berkeley, said after it was over. "I wasn't sure if this would work, seeing this weird bill at the Greek Theater. But it worked. Oh yes, I'd say it worked."

The show was the first of two holiday-weekend appearances by many of the same bands. On Sunday, a similar lineup played in Irvine, Calif., for the This Ain't No Picnic festival.

About 3,000 people, many of them 30-somethings, in styles ranging from standard-issue punk rock to cardigan sweaters, were here for Friday's show on the University of California, Berkeley, campus.

They wandered in and found their seats during early sets by local punk-rockers Bratmobile as well as experimental duo Scarnella and the rock bands Rocket From the Crypt and Superchunk. As fans spread blankets on the grass or staked their places in the concrete "pit" at the bottom of the open bowl, the bands played short, tidy and relatively catchy sets, with fast turnarounds between acts. Many bands shared equipment to save set-up time.

The afternoon lengthened the shadows across the open arena as Guided by Voices got ready to take the stage. The Dayton, Ohio, guitar-rock band has a fervent fanbase, which was present down front in strong numbers by the time the band's famed cooler full of beer was carried onstage. The crowd cheered, the band came out, swung into "Submarine Teams" (RealAudio excerpt of Pollard version) — from frontman Robert Pollard's most recent solo album, Kid Marine (1999) — and people started dancing. Clutching a bottle of beer in his left hand and the microphone in his right, Pollard executed odd little karate kicks as he sang.

"These guys are like the Replacements of the '90s," Charles Turner, 32, of Berkeley, said. "They're loud, they get totally drunk onstage, and folks either love them or can't stand them. Of course, I love them."

The lawn area at the rear cleared out as still more people flocked to the floor in anticipation of Sleater-Kinney's set. Dwarfed by the huge, open stage, guitarists Carrie Brownstein and Corin Tucker, along with drummer Janet Weiss, did their best to fill the space. After a self-conscious start ("It's kinda cold up here. And it's so ... big," Brownstein said), they found their footing.

Encouraged by the crowd's roars of approval, there was an imperceptible shift, and as they tore into "The End of You" (RealAudio excerpt) the trio's presence somehow leapt outward from the stage. All eyes in the arena were focused on the three small figures in black.

Brownstein's and Tucker's vocals stitched together the pounding drums and two-guitar attack of their stripped-down sound. Their voices floated in and out of each other's, sometimes harmonizing in contrast, sometimes so alike as to be inseparable as they communicated both fury and vulnerability in their shrieks and whispers.

A tiny mosh pit sprung up in the first few rows, and between songs Brownstein sweetly admonished the crowd: "Remember now, no moshing ... Jump this way," she said, with a quick up-and-down pogo demonstration.

With the crowd in the palms of their hands, Sleater-Kinney settled into their stride. "OK, we're adjusting to this big outdoor thing," Brownstein said at one point. "It's like a big garden party!"

They closed their set with a roaring, screaming version of "Dig Me Out." Adhering to Brownstein's dancing instructions, the entire packed floor of the arena seemed to bop as one body, looking from above like a sea of deliriously bobbing heads.

Screams for an encore went unheeded, and the trio left the stage as the sun disappeared completely.

Strolling onstage without a word, Sonic Youth picked up their instruments and launched into a long, spacey instrumental vamp. The crowd, wiped out from the afternoon's sun and the poppy, noisy music that had come before, seemed stunned by the reverb-heavy sound. Sonic Youth used the evening's darkness to their advantage, their minimalist stage show enhanced by blue and orange lighting. The crowd stood and watched, swaying slightly.

Their between-song patter was limited to comments such as, "We're called Sonic Youth, and we're from the Northeast part of this country." The band's wall-of-sound discord put the evening on a decidedly abstract curve. Playing at times with three guitars and no bass, the quartet favored drawn-out, spooky jams over its more accessible material.

"This is nothing," Thomas Trillin, 34, of San Francisco, said. "I've seen them do 40-minute songs that consisted mostly of Thurston [Moore] hitting his guitar with a drum stick. This is downright catchy in comparison."

Guitarists Moore and Lee Ranaldo, Kim Gordon on bass (and sometimes guitar) and drummer Steve Shelley created extended jams that had alternately soothing and unsettling effects. Overlapping Gordon's whispery, ragged vocals, Moore literally danced back and forth on his effects pedals in the multicolored lights, producing guitar sounds ranging from a chain saw to a car's engine to a watery ultrasound heartbeat.

It may, however, have been Sonic Youth's last chance to make some of those sounds. On Saturday, a truck carrying sound equipment and the band's guitars — many of them customized to unusual specifications — was stolen from outside an Orange County, Calif., hotel, according to an e-mail posted by Ranaldo. The band played at the This Ain't No Picnic festival with borrowed equipment.

Sonic Youth's faster numbers, including "Sugar Kane" (RealAudio excerpt), got Friday's crowd moving a bit, though the band broke that song down into a 10-minute cycling swirl that tapered down to near silence before crashing back into the finale.

Sonic Youth's hypnotic discord was an aural lullaby for the tired crowd, as the arty noise-rockers wound down the evening and sent people on their way.