Modern Immaturity : First Green Day sells a ton of records, and now two of the three guys are married dads. Do we have to call them the anti-punks? Well, it’s not like they’ve really grown up. Not by a long shot.

Billie Joe Armstrong, the singer for the rock band Green Day, is spitting. Not at anyone, fortunately, and not for any particular reason.

The type of spitting Armstrong is doing backstage at Nassau Coliseum is apparently referred to in the fifth-grade vernacular as “hawking loogies”--accumulating masses of saliva and phlegm in his mouth and then ejecting them in a deliberate, almost artful manner. It’s spitting as a form of casual entertainment.

Oh, well--boys will be boys. And the members of Green Day, who will play the Pond of Anaheim on Dec. 12 and the Grand Olympic Auditorium on Dec. 13, are definitely boys.

Never mind that they recently released their fourth album, “Insomniac,” the much-awaited follow-up to “Dookie,” the 1994 collection of catchy, punk-flavored odes to Gen X angst that sold 8 million copies in the United States alone and made them MTV icons. Or that they’ve each reached the decidedly post-adolescent age of 23. Or that Armstrong and drummer Tre Cool are married and have become fathers in the past year, and bassist Mike Dirnt has gotten engaged.

In both looks and behavior, these guys could still pass for a bunch of food-fight instigators at your local high school cafeteria.

That said, at least two of these men seem to have their more sober sides. Cool, as his hysterical shock of kelly-green hair would suggest, is the group clown. Ask him a serious question and you’re likely to be answered with a wisecrack--several, in fact. In contrast, the skinny, high-cheekboned Dirnt tries to respond to most queries with some degree of thoughtfulness. He’s the most earnest and polite of the three.

And Armstrong? If he’s bored with a topic, he’ll just zone out. Or spit. But if discussion turns to a matter he deems important, like Green Day’s image, he’ll abruptly interrupt Cool’s snickering to speak his piece.

“We’re only a band,” Armstrong begins, his doe eyes widening. “We’re not bringing a scene or a counterculture with us. All we ever wanted to do was to play rock ‘n’ roll, music that people can relate to. We come from a background of punk rock, but we’re not walking down the street with a shopping cart with ‘Punk Rock’ on it, you know?”

Armstrong is addressing a dilemma that has faced punk-influenced bands from the Clash to Nirvana: How do you sell millions of records and retain an anti-Establishment cachet? It’s the Catch-22 of alternative rock. If your music is good enough to attract a sizable cult following, the industry hounds swoop in, sign you up and try to sell you to the masses. If you prove popular with the masses, at least some percentage of the cult following is going to accuse you of selling out.

“We never went around waving a punk-rock flag,” Dirnt reiterates. “We come from a certain area, and we still hold a lot of the values that we started out with. But there came a time when Green Day became its own entity, and when its show outgrew certain clubs, and we had to take things to another level.”

T he certain area that spawned Green Day is a blue-collar Bay Area community called Rodeo. Armstrong and Dirnt were childhood friends there, united by the sort of working-class adversity that created punk in the first place.

Armstrong is the youngest of six children. When he was 10, he lost his truck-driver father to cancer.

Dirnt was born to a heroin-addicted mother and then adopted by parents who divorced when he was 7. After a short, confrontational stay with his adoptive dad, Dirnt wound up living with his mom, who was barely able to support him and his older sister. The sister left home at 13, and Dirnt followed suit when he was 15.

As teen-agers, Armstrong and Dirnt took refuge from their woes at a local club called the Gilman Street Project, where bands copping the sound and attitude of British punk rock would perform for disaffected, impressionable kids. (Armstrong is to this day described as singing with a phony Cockney accent.)

Inspired, the two buddies formed their own band, which they called Sweet Children, and began cultivating what would become a devout following at Gilman Street.

After Dirnt graduated from high school and Armstrong dropped out, the two settled into a squat in nearby Oakland. In 1990, their group, by now re-christened Green Day and featuring a fellow named John Kiftmeyer on drums, released its debut album, “39/Smooth,” on the Berkeley-based independent label Lookout! Records.

After a cross-country tour that the neophyte musicians booked themselves, Kiftmeyer bailed. Enter Cool, a.k.a. Edwin Wright III, who had grown up a close neighbor of Lookout! founder Lawrence Livermore (real name: Lawrence Hayes) in the mountains near Mendocino and had been tapped at age 12 to play in Livermore’s band the Lookouts, another Gilman Street favorite. With Livermore’s approval, Cool joined Green Day in time to appear on the group’s second album, “Kerplunk,” in 1992.

In 1993, Green Day was signed to Reprise Records, a division of Warner Bros., by Dave Cavallo, a staff producer and senior vice president of artists and repertoire. With the group, Cavallo co-produced both “Dookie,” which ended Green Day’s affair with the anti-pop Gilman Street crowd, and the new “Insomniac.”

Now Cavallo and the group must confront a new challenge as the charges of selling out fade away--the challenge of selling up . Can “Insomniac” meet the outrageous commercial standard set by “Dookie”? And if not, will Green Day be dismissed by the industry as just another flash in the pan?

Many industry observers thought that Green Day was overexposed with “Dookie” and warned that there might be a large fan defection. Initial sales of “Insomniac” have been a bit shaky. Though the album entered the charts strongly, it has fallen to No. 25 after just five weeks. Estimated U.S. sales to date: about 500,000.

“I look at Green Day’s career from a long-term view,” Cavallo stresses after pointing out that “Insomniac” has enjoyed strong sales worldwide during its first month of release. “I think they’ve made a harder-rocking, less commercially oriented album this time, one that might not appeal to the masses like ‘Dookie’ did. But they’ve laid a good foundation by doing this. For their next album, they’ll be able to do anything they want.”

Gary Bongiovanni, the editor of the concert business weekly Poll-star, is also bullish: “In terms of their ability to sell concert tickets, they’re continuing to show great strength. They’re definitely a band on the rise. And they’re still keeping their prices low, so they’re making less money than they could.”

Indeed, all 12,000 tickets for Green Day’s concert at the Pond of Anaheim sold quickly, and a show was added at the 5,000-capacity Grand Olympic Auditorium.

But if the members of Green Day themselves consider it a prior ity to remain in the pop stratosphere, they’re not letting on.

“We’ve already surpassed any expectations we ever had,” Dirnt says. “I mean, I would have been happy if we’d sold 150,000 copies of ‘Dookie.’ I would have been ecstatic.”

“If we don’t sell as many records this time, it’s not a big deal,” Armstrong agrees. “Whatever, you know? So what?”

As the somewhat more socially conscious, issue-oriented songs on “Insomniac” would suggest, the singer has weightier stuff on his mind these days. Like fatherhood.

“Yeah, becoming a parent influenced my writing,” says Armstrong, who pens Green Day’s lyrics. “From an emotional standpoint, that’s true.” He adds that his 8-month-old son, Joey, and Cool’s 10-month-old daughter, Ramona, will, along with their mothers, be joining the group on the road for at least the immediate future.

“Right now, it’s easy to keep track of them, because they’re not walking yet. They’re too little to listen to the music, though,” he quickly notes. “It’s too loud.”

Too loud? Is Armstrong turning into a concerned dad? Don’t be alarmed. The boys in Green Day seem in no immediate danger of becoming old geezers--or even responsible adults, by most people’s standards. Armstrong was arrested and fined last week for mooning an audience in Milwaukee, and he and bandmates are as enthusiastic as ever about their use of drugs such as pot and speed. (“How else are you gonna stay up for four days?” Cool says with a shrug.)

And, says Armstrong, the main ingredients for a Green Day jam session are still “a small room, a lot of beer and loud music.” In other words, Joey and Ramona won’t be encouraged to attend anytime soon.

“They like Fisher-Price music, anyway,” Cool quips. Yuk, yuk. Or as another arrested adolescent once put it, huh-huh , huh-huh .*

* Green Day plays Dec. 12 at the Pond of Anaheim, 2695 E. Katella Ave., Anaheim, 7:30 p.m. Sold out. (714) 704-2400. Also Dec. 13 at the Grand Olympic Auditorium, 1801 S. Grand Ave., 7 p.m. $17. (213) 749-5171.