There was a time when John Cougar Mellencamp would tell you his songs were about nothing and meant nothing, an appropriate stance for a midwestern rock poseur whose defiant "Wild Ones" esthetic was summed up on one album as "Nothin' Matters and What If It Did." Mellencamp was a rock 'n' roll brat, nicknamed the Little Bastard, the embodiment of the petulant small-town punk finding release through noise.

Some folks bought the act, though his debut album sold fewer than 12,000 copies.

But things began to change with 1982's "American Fool." Buttressed by "Jack and Diane" and "Hurts So Good," two catchy and concerned teen anthems that became top-five hits, it ended up as the year's bestselling album. Last year's "Uh Huh" had three more hits, including the bracing "Authority Song" ("I fight authority, authority always wins") and "Pink Houses," a sobering vignette of mounting unemployment and farm foreclosures in Mellencamp's Indiana -- concerns that would lead to his organizing September's Farm Aid concert with Willie Nelson and Neil Young.

Mellencamp's identification with the working class was reinforced by the recent release of "Scarecrow," one of the best albums of 1985 and a commercial success as well (it's now No. 3 on the charts). Its raw, emotionally direct songs deal with the plight of farmers and factory workers, America's disappearing ideals, family and small-town values, the importance of tradition.

Suddenly, Mellencamp's songs are about something and mean a lot. As he sings in one, "You've got to stand for something or you're gonna fall for anything."

"For a long time I was just a guy in a band in a bar, right?," he says quietly. "We had pierced ears, black leather jackets and tattoos. My only responsibility was to myself." He was resting up in the Plaza Athena one afternoon last week before a sold-out Madison Square Garden concert. (He ended up playing that concert for free. After a 25-minute delay to get the sound system to work, Mellencamp told the crowd, "Listen, everybody. I feel so bad about this, the show is on me. If you have your ticket stubs, you've got your money $17.50 per ticket back." He played the Baltimore Civic Center Saturday night.)

" 'Jack and Diane' was the first thing that made me think maybe somebody was listening. People were coming up to me and saying, 'This means so much to me' and I was going 'Ah, come on . . .' It was hard for me to take it seriously, because I'm not Bob Dylan -- that's who you pay attention to. Then serious things started happening and I quit playing in bars and started having more time to myself and realized I wasn't that happy doing what I was doing."

Mellencamp's unruly hair still drapes across his face, but he can see clearly now. "I had a big chip on my shoulder about everything -- don't get me wrong, I still do. I was ready to beat up anybody, argue with you, walk off your TV show" (as he did on "Nightwatch" when he felt the interviewer was asking stupid questions).

Ironically, "Jack and Diane" -- a moving ditty about "two American kids growing up in the heartland," trying to hold onto the spirit of being 16 and finding that "life goes on long after the thrill of living is gone" -- almost didn't make it onto "American Fool."

"I felt it was too corny, too stupid, too pansy," Mellencamp remembers. "I had a hard time with that because I saw myself as some romantic macho, a cowboy coming into town on a silver bus, yelling the loudest and getting the hell out when the trouble began. It was a dumb, romantic idea of what I thought rock 'n' roll was about.

"Someone once said, 'There's always one loudmouthed kid with a guitar ready to screw everything up.' I thought, 'That's me.' " And of course it was, which locked Mellencamp into his minor talents -- until he could find a major voice.

How did it happen? "I'm just a guy from Indiana. I don't have a lot of talent, never professed to have a lot of talent," he says bluntly. "But I've had the opportunity over 10 years to make records and be in front of people, and I'm getting better at what I do."

Over the past three albums, as his lyrics became more populist and direct, as his music eliminated its pretentions and stripped down to basics, and as the blue-collar identifications became stronger, Mellencamp has found himself portrayed as a kind of straw Boss. "I'm not great," he insists, "I'm not Bruce Springsteen, I'm not Bob Dylan. I'm John Mellencamp and until I can get that point across, then that's my problem.

"People want to like me, but it's not cool," he laughs, referring to his entrance into the record business 10 years ago under the tutelage of idolmaker Tony Defries, who turned David Jones into David Bowie and who tried to turn John Mellencamp of Seymour, Ind., into "Johnny Cougar, the cat of rock 'n' roll." They soon parted company, and Mellencamp has since dropped the "ny" and reclaimed his surname, but the hype remains burdensome.

For years, Mellencamp's albums and behavior reinforced rock's worst conventions. Now that he's 34, he has reassessed his responsibilities, progressed to adult concerns. "I've written a lot of songs about teen-agers," he says, "but it would be very untruthful to continue writing songs about the street . . . I'm married, I've got three kids. The only street I see anymore is what my 15-year-old daughter Michelle tells me about, and her reality is very different than mine was."

The change is perhaps most evident in the distance between the caustic "Dream Killin' Town," one of his early songs, and the new, near-elegiac "Small Town," a coming to terms with the characters and situations encountered growing up in any small town, even one that became a toxic dump site and at one time had the highest per capita murder rate in the country.

Reminded of "Dream Killin' Town," Mellencamp laughs. "I haven't even thought of that song for years. Perhaps I'm starting to understand my own reality and not Bob Dylan's reality; that's where I stole the idea for that song, all those words running together . . . 'Small Town' is from me, has nothing to do with Bob Dylan or anybody else.

"I hated Seymour," he continues. "The first time I came to New York I was embarrassed that I was from that town because the first thing everybody said to me is, 'What kind of accent is that?' Accent? I didn't know I had an accent. But let's face it, I'm a hillbilly and there's nothing I can do about it. I tried to hide that and disguise it. But in the last 10 years, this country's changed a lot. I think it's people my age realizing that you can go to any town in the world, but you're still home inside your head."

Growing up in a blue-collar town, Mellencamp seemed to inhabit an S.E. Hinton novel. Like his fellow Hoosier, James Dean, he was a rebel without a pause, gleefully following all the conventions and rituals -- skipping school, drinking, smoking grass, drag racing, girl chasing. At 17, he was married, at 18, a father.

He used to think his Hoosier neighbors were "a bunch of bumbling, foolish people, 'cause surely there's a better world somewhere else. But the more I went around and the more I had a chance to look at them and myself and other people, the more I realized that just wasn't the case. I had some adolescent idea of what they were like and I was wrong about it. What a surprise it was to find that the most interesting people I've ever met live in my back yard."

The stripped-down focus of the last three records reflected another change. "Woody Guthrie said, 'Everybody should be able to play my songs,' and I agree with that spirit," Mellencamp says, "the spirit that the Human Beinz had on 'Nobody But Me.' I understood that spirit, I felt those songs when I was a kid, the energy. I understood a lot of the American things. I'm finding out now that I don't understand the Who anymore; they were a lot more British than I ever thought. I don't understand 'My Generation' at all anymore; I wonder what the hell that song was about. 'Everyday I get in the queue.' I didn't know what the hell a queue was. I'm obviously influenced by the Rolling Stones, but I understand less about their songs now than I ever did.

"Garage -- that I understand. I ought to."

With their refocused lyrics, Mellencamp's new songs resonate with a deeper truth, but he claims not to be convinced of their worth. "It's not an inferiority complex, it's just knowing yourself," he insists. "I'm not the most talented guy in the world, let's face it. I flunked sophomore English three times. My way with the language is not that great. It's not as passionate as Bruce, not as intelligent as Bob Dylan, but what it is, I think, is very honest. And I think that is the connection I make with people."

Although Mellencamp was one of the key Musical Majority figures speaking out against censorship of song lyrics, he's cleaned up an act whose flow of obscenities once left a trail of outrage. "I've got a cruddy mouth. I was brought up around men who swore. I swear. That's always been part of it. Not any more. I don't like to have my picture taken smoking, I don't allow guys to bring alcohol on stage. Even little things that used to not concern me in the least -- I used to smoke while I sang. That's what rock 'n' roll was to me; it's not that way anymore. And to play like it still is, I'd be a big fool."

Even as he rejects corporate sponsorships of his tours, he's looking for projects. There's a script he cowrote with Larry McMurtry ("The Last Picture Show," "Terms of Endearment"), but the studios say it's too downbeat and Mellencamp won't sing in a movie. Still, film is something he wants to slip into.

"Movies can say a lot more and say it better. There's not all the wrong connotations being put on the words, like 'Hold On to 16.' If I'd shot that in a movie I could have made it very clear what I wanted to say. Movies like 'Hud' mean a lot more to me now than 'Street Fighting Man.' "

So Mellencamp's all-American now; no longer self-centered, just centered; living and working out of Bloomington, Ind. He's focused, putting aside the music business at a certain time each day to be with family and friends -- a strand of real life running through the fantasy of rock 'n' roll.

He named his new daughter Justice, after one of the songs on "Scarecrow" ("I wanted to name her Baby Doll, after Tennessee Williams. I thought, well, they'll just call her babe"). The album, and his concerts, open with a lullaby sung by his 85-year-old grandmother. His father works for him, as does his first wife, Priscilla. Priscilla is a close friend of his current wife, Vicki, whom he married five years ago. Symmetry.

He's even at ease under the ever-present shadow of Springsteen. "I can't help it," Mellencamp shrugs. "I'm not going to change. I'm going to do what I'm doing and hope I get better at it. If that's my fate, it's the same fate the Small Faces had with the Rolling Stones, the same fate James Dean had with Marlon Brando.

"It ain't that bad. Don't act like it's the end of the world. I'm doing fine."