POP MUSIC : Gourds a-Flyin’ : Smashing Pumpkins leader Billy Corgan doesn’t really expect the band’s alternative rock to take anyone completely by surprise. He just unleashes his emotions and tries to deliver a sonic assault diverse enough to match

At first glance, Billy Corgan hardly comes across as the latest giant of the college/ alternative rock world. He’s not darkly handsome and elusive like Nirvana’s Kurt Cobain, nor outwardly rebellious and gritty a la Pearl Jam’s Eddie Vedder.

The 6-foot-plus singer, in fact, appears as soft and vulnerable as your favorite stuffed animal. His short, chestnut-colored hair isn’t cut in any of the trendy styles of the day, and his round, brown eyes seem placid.

But spend any time talking to Corgan, 26, and you gradually sense the layers of anger, frustration and self-doubt beneath his steady, soft-spoken exterior--the same kind of turbulent emotion found in the music of Smashing Pumpkins, the acclaimed band that he leads.

“Siamese Dream,” the album that recently turned the group from college/alternative scene to mainstream bestsellers (“Dream” has sold 500,000, and the band headlines the Hollywood Palladium on Thursday and Friday, then moves on to UC Santa Barbara on Saturday and San Diego’s Crosby Hall on Oct. 26), is filled with moody dynamics that shift from contemplative to furious.

Corgan uses heavy Black Sabbath- and Jimi Hendrix-style riffs en masse, then adds touches of psychedelia and Cheap Trick-like vocals. The blend is so sonically diverse, it feels like a collision of a dozen separate emotions.

But the Pumpkins’ music isn’t all supercharged. There are dreamy interludes--rest stops, if you will, in the restless journey. The whole album is immersed by producer Butch Vig (who also worked on Nirvana’s “Nevermind”) in fuzzy textures that give it a raw edge.

“My emotions are represented as direct on the album as anyone can represent their feelings in music,” says Corgan. “I’m not just expressing one thing at a time. I’m expressing love, bitterness and anger all at once. I don’t think I’ve ever expressed it as deep as it can go.”

Putting those feelings on record wasn’t easy for Corgan--especially after the high expectations raised by the group’s 1991 debut album, “Gish.”

Relentless waves of unsolicited advice on how to live up to those expectations poured in from critics, fans, peers and record-company types and had Corgan unsure of exactly where to go.

“I had everyone telling me what to do, and there’s only so long you have a resistance and security to feel there’s a difference between your opinion and everyone else’s,” he says, still sounding dazed by the whole process.

“Suddenly, you feel this great pressure to make an amazing album, one that’s not only an amazing Smashing Pumpkins album but will also become the next album to set the world on fire.”

The pressure on Corgan as he began planning the follow-up album, “Siamese Dream,” was so intense that he suffered what he describes as a nervous breakdown.

“There’s been a lot of time between albums because I flipped out. I couldn’t function,” admits Corgan. “I didn’t want to leave the house, I didn’t want to talk to anybody. I couldn’t get along with the band. It was the complete breakdown of everything I had around me, everything that gave me some structure to work in.”

During this period, the band--which also includes guitarist James Iha, bassist D’Arcy and drummer Jimmy Chamberlin--suffered its own breakdown.

“When my relationship with the band in all essence collapsed, it was like part of me died,” Corgan says. “I went through this weird mourning, like almost mourning the loss of what I thought I was. I was suicidally depressed. If the concern was to succeed and make great art, I definitely wasn’t going to do it the way I was going.”

But time helped him combat his anxiety.

There was no dramatic moment in which he reclaimed his musical future. He simply says he woke up one morning and felt as if he could cope again.

“Somehow, things seemed calm again and I told myself, ‘Hey, this is only rock ‘n’ roll.’ ”

Corgan grew up an hour outside Chicago in a suburb whose name--Glendale Heights--amuses him. “I have no idea why it’s called that,” he says, flashing a trace of his subtle humor. “What would you name a flat piece of land with trees?”

As a youngster, Corgan was surrounded by music. His father was in a soul band, and that meant there were lots of albums around the house by groups like the Temptations. Corgan himself also loved Top 40 radio, listing bands such as Chicago pop cutups Cheap Trick and R&B;’s Earth, Wind & Fire as particular favorites. His rock heroes also included Black Sabbath and Led Zeppelin.

“I grew up listening to all this stuff at the same time,” he says. “I relate back to it now and realize I had no prejudice when it came to music. I just listened to it all. One song sounded good, one bad. The genre didn’t bother me. It wasn’t until my teens that I found it wasn’t cool to listen to certain stuff. Those early feelings are part of what guides my sensibility with the band now.”

By age 15, Corgan was playing guitar. “I wanted to be the world’s greatest guitar player,” he says now, laughing at his own early innocence. “I practiced like eight hours a day for four years before deciding this is a really bad idea. God knows why it took four years to figure that out.

“If you’re the greatest guitar player in the world, who really cares? Nobody--other than other guitar players. Besides, every guitar player I know is a geek, and so who am I trying to impress?” He laughs. “That was around the time I discovered alternative music. It opened up a whole new world, and it was not really about being able to play.”

Redirected, Corgan then started writing songs that fused seemingly incompatible elements from the far-flung borders of rock and pop.

By 18, he had started his first band, but it was short-lived. He spent most of the next two years holed up in his room in Chicago recording demos. Finally satisfied that he had good material, he formed Smashing Pumpkins in 1988.

The quartet played around Chicago and put out a single in 1990 on the independent Sub Pop label. The record--a piece of scratchy acid-rock called “Tristessa”--led to a contract with a larger independent, Caroline.

On “Gish,” the widely acclaimed debut album, the Pumpkins mixed thick, heavy acid-rock, gum-cracking pop and messy wads of grunge. It was a breaking-down of musical barriers that was still rare at the time.

“We’ve reached a somewhat finite point with rock ‘n’ roll,” Corgan says of his diverse tastes. “There’s really not a lot more room to go. What am I gonna do? Throw my guitar out the window and start programming a synthesizer? We basically take what’s happened and mutate it so it’ll sound different.

“Any band that gets talked about as being groundbreaking or revolutionary these days is not really that revolutionary.

“I was talking to my dad about Jimi Hendrix and he was saying, ‘You gotta realize that when I first started playing guitar, if you got distortion in your amp, you took it back to the shop because you thought something was wrong with it. Then this guy puts out an album one day and is doing everything completely wrong, but it sounded so right.’

“You have to remember the context it happened in. It blew minds and took everyone by surprise. Really, nothing that goes on today takes anyone by surprise.”

“Siamese Dream” debuted in August at No. 1 on CMJ’s New Music Report, a weekly guide to the most popular records on the college/alternative scene, and stayed there for eight weeks. But the band is still viewed with suspicion by some purists in the indie-rock world.

It’s the same thing that happens with other alternative bands that commit the ultimate indie sin of becoming famous. But Corgan seems especially troubled by the accusations that he has sold out.

“I think most of those problems arise out of the fact that I don’t have the proper indie credentials,” he says. “I didn’t play in some seminal band where five people bought the record, I wasn’t a roadie . . . that kind of rags-to-riches story. It didn’t happen that way.

“Everyone can pretend all they want, but when a band sells a lot of records, it’s no accident. A band has to make an album that’s accessible, it has to make videos and so forth. When someone goes, ‘Oops, I accidentally sold 3 million albums. I’m so embarrassed,’ they’re full of it. In my case, I said I wanna do this and do it right, so we worked really hard to get where we are today.”

In the process, he said, he made exactly the record he wanted to make.

“There was a part of me that didn’t want to depart too far from the first album, not just because of what people would think but because it sounded pretty distinctive,” he says.

“It felt comfortable--Pumpkin-esque or that Pumpkin sensibility. The next album will probably be a lot more radical of a departure because I feel like I’ve captured what I wanted.”