Bang on a Can, the New York circle of composers whose trademark 10-hour marathon debuts at the Live Arts Festival on Sunday, maintains the right to go to extremes.

All of them.

Some moments might be extremely pretty. Others enter less-explainable extremities such as the extraterrestrial Sun Ra Arkestra, the often-ethereal So Percussion, indie rock band Normal Love, Asphalt Orchestra playing Frank Zappa, and the marathon's house band, Bang on a Can All Stars. Hosting the event at World Cafe Live are the three increasingly eminent composers who founded the marathon in 1987, Julia Wolfe, Michael Gordon, and David Lang.

"Philadelphia is such a beautiful old historic city that, in a way, it's more radical to bring this into that environment," says Wolfe, who grew up in nearby Montgomeryville.

At least Philadelphia has fewer outside distractions than New York over the 2 p.m.-to-midnight duration. "We try to make it difficult for people to leave," said Kenny Savelson, executive director of Bang on a Can.

Does he hide the audience's shoes?

"We try to be as entertaining as possible," he assures. He also minimizes information about the individual artists so the audience can't prioritize.

Staying for the whole thing is a point of honor in some circles, an act of immersion for others, and a defiance of practicality for all - particularly those producing the event. Sets range in length from 12 minutes to an hour, meaning that 100 or so musicians will be trooping in and out of the cozy World Cafe Live, along with sound and stage staff. To give everyone a sound check, Live Arts bought out World Cafe for the night before, which happened to be an expensive Saturday. The production price tag is $125,000 - high for the Live Arts Festival, but reasonable considering that some of New York's and Philadelphia's best new-music groups will be present.

"We've mostly been oriented around dance and theater," said Nick Stuccio, the Live Arts Festival's producing director. "All of the work over the years has had some music component, there's been a concert here and there, but we've been remiss. ... "

Yet there's little danger of shock factor. Philadelphia's Relache ensemble pioneered rock/jazz/classical fusion for decades. In recent years, Bang-related appearances here included the Asphalt Orchestra - an offshoot ensemble that's sort of a cutting-edge marching band - in a guerrilla noontime performance at 30th Street Station. The All Stars have appeared at the Kimmel Center. And the many Bang-oriented recordings on the Cantaloupe label are hard to miss.

The marathon's arrival, however, grew out of a series of chance meetings and conversations between Stuccio and Bang development director Tim Thomas - the most important at a small-town barbecue in the Catskills.

"It was in the middle of nowhere, a town [Andes, N.Y.] that's a block long," Stuccio recalls. "And we weren't on the main drag but some random parking lot where they were having the best-looking baby contest. . . . "

That's not out of character with Bang on a Can's history, in which casual moments may have momentous consequences. The three founding composers met at Yale, migrated to New York in the late '80s, and began the marathon as sort of a "happening" whose length ballooned due to all the pieces they wanted to hear, both their own and by others.

Though composers can be fiercely partisan, the first marathon brought together arch-minimalist Steve Reich, uber-serialist Milton Babbitt, and mystic philosopher John Cage. The big question in that first year was what to call it. Wolfe said, "Let's just say it's a bunch of composers banging on a can."

"That's it!" exclaimed Lang. "That's who we are!"

The problem, at times, has been convincing foundations and donors of that. "A few times we had to explain that we aren't Stomp," the Off-Broadway show, Wolfe said. "Also, people expected the marathon to be just percussion music. But what we wanted to do is get rid of any formality and to crack open the audience for this kind of music."

The Philadelphia accent to the programming - not just with the Sun Ra Arkestra but also with the contemporary music choir The Crossing - is considered a natural part of exporting the marathon. Yet one has to wonder how the manic brass writing of the Asphalt Orchestra, the severe Dutch minimalism of Louis Andriessen, and the massed voices of The Crossing will blend. Clearly, the common denominator is more a matter of attitude than outward sound.

"It's a melting pot. We're a bit like mad scientists putting all of this in a room with the audience and creating a new experience," said Savelson. "You get to hear it all in one shot. And it creates a conversation. That's the important thing."

One wild card, says Stuccio, is when it will end and who all will end up onstage together. "If the party is rolling, and the music is great, I'll authorize overtime" pay, he said.

Another such card is the collaborative efforts of the three founding composers. Jointly written pieces are rare in music history. Yet Wolfe, Gordon, and Lang have all contributed their own movements to the hour-long oratorio Shelter - each meditating on what that word means, in conjunction with a visual component by videographer Bill Morrison.

Wolfe, for one, riffed on porches - "when people would sit on them and drink lemonade, and how little by little the porch was enclosed with screens and then walls," she said. Lang loves to set lists to music, and requested a home-related one from librettist Deborah Artman.

Luckily, the three are used to consulting one another on their music, which is particularly easy for Gordon and Wolfe since they're married. "I'll say, 'Listen to this!' And he'll shake his head. And I'll get mad and say, 'I've been working on this all day!' " says Wolfe. "Maybe I'll realize he's right. Then sometimes I convince [him] that I know what I'm doing . . . "