MONICA IS MORE than just a face, more than just a voice. The 18-year-old R&B star is already an accomplished singer. She doesn't just hit the notes; she fills them with her personality.

Whether it's her breakthrough single, 1995's "Don't Take It Personal," her chart-topping duet with fellow teenager Brandy, "The Boy Is Mine," or the follow-up hit, "The First Night," Monica comes across as a young woman who knows just what she wants. Addressing a rival or a pushy date, she lays down the law -- not with hysterical anger or desperate pleading but with the confidence of someone who expects to get her way.

"That's just part of my character," she explains, "it's not something I practiced. Being self-assured is something my mother has always been. I really pattern myself around a lotof things she does and a lot of ways she acts, and that seeps into my career. A lot of girls grow apart from their mothers, but we're so much alike and we've always been so close that I couldn't imagine it any other way.

"The one thing I try to imitate is her self-control. No matter what the situation was, she would always approach it with a sense of calmness. That's an area I always had a problem with; my temper was a little bad. I've learned not to let other people make me react to them and the things they do. I've tried to maintain that over the past few years."

One challenge to her self-control has been her alleged feud with Brandy. Monica, who appears with 98 Degrees, Tatyana Ali, No Authority and EYC as part of the All That Music & More Festival on Saturday at the Nissan Pavilion, denies that any quarrel has ever existed. But that hasn't stopped the media and Internet forums from speculating about the rivalry.

"The strangest thing is they never could see us together," complains an exasperated Monica. "She was in the North and I was in the South, and we never saw each other except at awards shows. We were two young, black women doing positive things, and they just harped on this imaginary fight. It just got tiresome for both of us. We each have our own career, our own style."

What are those differences in style? "I would never presume to categorize her style. My approach, I feel, is reality. I like to sing about things that I experience, and I sing them with a lot of feeling. If I didn't experience it, I saw my mother experience it, and that makes my records very realistic.

"Plus, the South has a different way of singing. If you go to New Orleans, you hear people sing with extreme feeling. If you go to Georgia, North Carolina, anywhere like that, they have a lot of soul. But, then again, Whitney [Houston] comes from Newark and she has more soul than the whole industry put together."

She was born Monica Arnold in College Park, Ga., just outside Atlanta. She grew up singing in the nearby Jones Chapel United Methodist Church, and by age 10 she was singing with the touring group Charles Thompson and the Majestics. Also in the group were the sisters LaTocha and Tamika Scott, who later became the core of the hit R&B group, Xscape.

"Church built my entire style," Monica says. "The way that I sing is not something I was taught; I always sang with feeling because that's the way I sang in church -- from the bottom of my heart. When everyone around you sings the same way, you can't help but absorb it."

Monica was only 11 when she started entering local talent contests. She sang the same song every night, "The Greatest Love of All" by her idol Whitney Houston, and she won more often than not.

"That song always gave me freedom," Monica says. "I could always sing how I felt, because I love what the song says and the melody isn't cluttered with a lot of words. You can take off from the melody and give it your own spin. That's the sign of an honest, true singer, that's the kind of singing I enjoy most. You can express something even without words."

At one of those talent shows she was spotted by a local A&R rep who put her in touch with Atlanta's R&B guru, Dallas Austin, who has worked with everyone from TLC and Boyz II Men to Madonna. Austin signed Monica when she was 12, brought her into the studio at 13, and released her first album, 1995's "Miss Thang," when she was 14. When "Don't Take It Personal" and "Before You Walk Out of My Life" both topped the Billboard R&B charts, Monica became the youngest artist to ever score consecutive No. 1s.

"It was real easy for me to make the switch to secular music," she says, "because I only knew one style of singing, and that was singing with a lot of feeling. I didn't think I was giving up my Christianity to sing this other kind of music; it was just my way of showing my talents to the rest of the world. Each artist knows what he or she sings about and whether it's based on morality or not.

"When people work with me," she adds, "they realize the best thing they can do is write things I can relate to. They don't even bring me those provocative songs. They don't see me as an artist who sings about those lusty things. Those songs may be all right for someone else, but I have no plans to sing that kind of material.

"I like to hear other artists do it; it might even be my favorite song on the album. But I never saw myself in a G-string, singing about my rear end. I never had those ideas when I thought of myself as an artist."

The most ambitious song on Monica's current album, "The Boy Is Mine" (Arista), is its opening track, "Street Symphony," written and produced by Dallas Austin. Powered by surging strings, the song captures the familiar dilemma of an inner-city adolescent who must decide whether to follow or back off when a childhood friend gets entangled in the street life. Monica tells her old pal he has to choose between her and hustling.

"That song was based on an experience of mine that I don't really talk about," she confesses. "But it's something that a lot of young women experience. It's a reflection of how I felt about the situation. Dallas and I have always been really open. If, in the course of an album, I'm experiencing something that makes me upset, we'll sit down and talk about it. And this song came out of one of those.

"All of us experience someone we've grown up with who is doing something we don't want to get involved in. You have to love the person, it's true, but the person has to love you, too, and realize you can't get involved in that situation. It doesn't change how you feel about the person, but you also have to know how you feel about yourself. And that was the one situation that gave me a chance to know who Monica was."

MONICA -- Appearing Saturday at Nissan Pavilion in the "All That Music & More" music tour with 98 Degrees, Tatyana Ali, 3rd Storee, No Authority and others. * To hear a free Sound Bite from "The Boy Is Mine," call Post-Haste at 202/334-9000 and press 8112. (Prince William residents, call 690-4110.)