T he lobby of New York's Mercer Hotel is a haven of downtown chic - all angular furniture in shades of aubergine, with oblong oversize lampshades atop carved wooden posts. A wall lined with bookshelves displays volumes on Toulouse-Lautrec, Robert Mapplethorpe and Andy Warhol alongside studies of designers Vivienne Tam and Salvatore Ferragamo and anthologies on modernist architecture. The place is, as Gwen Stefani puts it, 'super frickin' trendy cool', the kind of hotel where everyone pretends not to notice when Nicky Hilton saunters past the reception desk.

But someone has taken notice of Stefani, lounging inconspicuously on a leather cafe chair on this late December evening. Stefani is done up in the luxe street style that has made her an international fashion icon: dark-wash jeans from her own L.A.M.B. label ('They look good whether I'm a little fatter, or not,' she says), a L.A.M.B. wife-beater [man's sleeveless vest], suede Christian Dior clogs that add 3in to her height and platinum-blonde hair extensions bubbling out from under a blue knitted ski cap. She slouches lower in her seat. 'There's this guy over there and he won't stop staring at me,' she says.

I turn around and see a toddler - big blue eyes, hair so fair it blends in almost completely with his scalp - gazing in our direction. Stefani giggles. 'The little baby,' she says. 'So cute.'

Stefani has always been the kind of songwriter who lives out her private dilemmas in public. 'Don't Speak', the song that sent No Doubt over the top in 1996, was about the break-up of her seven-year relationship with bass player Tony Kanal. In 2000, after four years of dating Bush frontman Gavin Rossdale, she made a video for No Doubt's 'Simple Kind of Life', where she ran wild in a wedding dress while singing, 'I always thought I'd be a mom/Sometimes I wish for a mistake.' The first single from her recent solo debut, 'What You Waiting For?', chronicles her baby lust - the 'tick-tock' refrain of the chorus, she says, was inspired in part by the sound of her biological clock.

During the three days I spend with her, her desire to have children is a continual theme, whether she's talking about how she never planned on being a pop star ('Before that, all I ever did was look at Tony and pray that God would let me have a baby with him'), or the joy of marrying Rossdale ('It's such a beautiful, magical feeling, I can't explain it. It's like having a baby. I can imagine what it might be like. But that love I've never experienced'), or her plans for the future ('I don't know what I'm going to do, but I've always wanted to do the family thing').

Like any successful woman on the mum track, she worries about the conflicts of career and family, although most women don't have to stress about the demands of dressing as fairy-tale characters in music videos. 'At a certain point I'm going to want to have a family,' Stefani says, 'and I'm not going to have time to be running around the world doing this shit and being greedy. I can always write songs. But can I always wear an Alice-in-Wonderland costume? I probably shouldn't. I can at home. I was thinking that when I have children, that I should always dress as a character for them, so they think their mom is Alice in Wonderland or Cinderella. It would be totally messed up!'

'I hope she chooses to do both things,' says Jimmy Iovine, chairman of Stefani's label Interscope, of the star's career and family ambitions. 'She can handle both. I think she would regret not fulfilling her potential as an artist. But her potential as a mom is equally as powerful.'

'This is the first time in a long time that I don't know what's gonna happen next,' Stefani says. 'As a famous person you think how you're gonna end it, get away and have a normal life. I imagine my children are going to save me from my vanity and be my passion and fill whatever fears I have of the amazing time I'm having right now being gone.

I don't want to drop off and not be on the radio or not be able to talk about myself for hours. I don't want it to go away. But at the same time, I never expected to be here in the first place.'

Disturbing but true: listen to US rock radio these days and you'll hear a woman's voice only if it belongs to Gwen Stefani or Evanescence's Amy Lee. Lee has sold a lot of records in the past few years, but Stefani is the only true female rock star left on American radio or MTV. 'She's toured from when she was 18 years old, playing small clubs, to playing small theatres, then amphitheatres and then arenas,' says Iovine. 'She is the only woman on pop radio right now who has toured with that vigour, and she's the only one who could as easily tour with U2, Green Day and OutKast.'

Almost 10 years after 'Just a Girl' hit the airwaves, Stefani has an instantly recognisable voice, an inimitable sense of style and an impact on popular culture on par with Madonna's. 'There will never be anyone else quite like her,' says Garbage singer Shirley Manson, who has known Stefani since the mid-Nineties and toured with No Doubt in 2002. 'She's got an extraordinary mixture of the elements that make a great pop star and the elements that make a great rock star. She's like the perfect Trojan horse: she seems very benign and wholesome, but underneath lurks an incredible toughness and powerful directness.'

Indeed, Stefani is one of the only Nineties stars who has managed to hold the attention of the ever-churning teen audience. Her solo debut album, Love, Angel, Music, Baby, sold half a million copies in its first two weeks. She recently scored a pair of Grammy nominations: one for 'What You Waiting For?' and one with No Doubt for their cover of Talk Talk's 'It's My Life'. (If she wins both, her Grammy collection will expand to five.) In December, she made her big-screen debut, playing Jean Harlow in Martin Scorsese's Howard Hughes biopic, The Aviator . And last night, she went to a party for her clothing line, which is now preparing its fourth collection for autumn 2005.

Love, Angel, Music, Baby is the kind of Eighties-style electro-dance album that Stefani grew up on in Orange County, California. It's so Eighties, in fact, that members of New Order are playing on 'The Real Thing', alongside collaborations with OutKast's Andre 3000, Dr Dre and Eve, the Neptunes, Dallas Austin and Linda Perry. 'Right now I'm all about trying things I've never done,' Stefani says. 'I'm a woman and I'm 35. I don't have that much time left to do this kind of pop record. Let's be real.'

The idea for the album, she says, came to her one morning during No Doubt's Rock Steady tour two years ago. She heard one of her favourite Eighties dance tracks, Club Nouveau's 'Why You Treat Me So Bad', turned to Kanal over breakfast and said, 'I want to do that song.' It was Kanal, after all, who had introduced her to that kind of music when the two were teenage sweethearts, before she turned him on to ska, before No Doubt had a record deal.

'I was super-ska girl when I met Tony,' she says. 'I wore only black and white and hoop earrings. Tony went to Anaheim High School, the big cholo [Mexican] school. He came over here from England at 11. He has Indian parents, and he was the first-born, so he didn't have any influences. He thought he was Prince. Because I had a crush on him, he turned me on to Prince and Lisa Lisa and Debbie Deb, and that stuff has always had a special place in my heart.'

When No Doubt got to the end of the tour in late 2002, the band was ready for a break. Stefani had just married Rossdale, Kanal 'had his first real girlfriend', guitarist Tom Dumont was engaged, and drummer Adrian Young's wife had given birth to their first baby. 'Everything started changing,' Stefani explains. 'All those years we were only committed to each other, but then we grew up. You could tell people in the band needed a break.'

The night before she is scheduled to perform at the 2004 Billboard Music Awards, Stefani sits on the couch in a Las Vegas hotel room looking like Alice in Wonderland on dressdown Friday. Her hair is held off her face with a thick velvet headband, and she's dressed in a black sweater, jeans and white sweatsocks. A keyboard with coloured tape marking specific keys sits next to the couch so that Stefani can rehearse the intro to 'What You Waiting For?' in her spare time. She starts by showing me a blister on her thumb that she got after one of the candles in her hotel room tipped over and spilled hot wax on to her.

'I can't stop playing with it,' she squeaks. 'I was in such a shit mood before you came,' she says. 'I'm really on my period right now. I'm so emotional. I'm gonna cry just talking about it.'

Many of Stefani's stories involve her either crying, or nearly crying. 'I'm really emotional,' she says. 'I don't fight with people - like, I can barely fight with my husband because I'll just start crying instead. I've learnt not to do that. Period week, I cry a lot. And the week when I was going to Anaheim to play my first show by myself, I cried on the way, because I was like, "This is surreal. Why does the first show have to be in Anaheim?"'

Gwen Stefani's parents - her dad is a marketing exec and her mum quit her job as a dental assistant to stay at home with the kids - still live in the same house in Anaheim where she grew up with her older brother Eric, younger sister Jill, and younger brother Todd. 'My mom and dad met at Anaheim High School,' she says. 'After they got married, all they wanted to do was have four children, and they did.' When the kids were still small, their parents would take them to bluegrass and folk festivals; one of the first shows Gwen remembers seeing was Emmylou Harris. 'She had just had a baby,' she says, 'and she took a break in the middle of the show to go feed the baby. I couldn't believe it.'

The Stefani kids still all live relatively close to home, and though Gwen says she's very close to Jill - the two call each other simply 'sister' - it was Eric whom she idolised as a teenager. No Doubt was his band before he recruited Gwen to share singing duties with the late John Sinclair, who committed suicide in 1987. Eric quit the group before Tragic Kingdom came out and now works full-time as a cartoonist. 'Everything Eric was into, I got into,' she says. 'He's supercreative, and he was this high-school cartoonist and had all these wild artist friends. I don't know if he really was cool or not, but he seemed cool to me.'

By comparison, Stefani says she was 'pretty lazy' and 'passive'. She had trouble with her grades at Loara High School and didn't even know if she was going to be able to graduate. By the time she got to Cypress College in 1987, she discovered that, even though she couldn't spell to save her life, she was getting pretty good at writing song lyrics. 'After Tony broke up with me, I realised I had something to say,' she says. 'When I started writing songs, it was like, "I'm a real human, I can do something."'

Love, Angel, Music, Baby, though, proved a major challenge to Stefani's confidence as a songwriter. Her original idea was to make an old-school dance album 'with Tony in his bedroom and the two of us singing in a microphone', she says. Jimmy Iovine wanted something bigger and pushed Stefani, pairing her with producers such as Dallas Austin and Linda Perry in hopes of striking chart gold. 'She was nervous about it,' says Iovine. 'It was her first time doing something without her band, and it was a big step. I said, "Let's just experiment and see what happens."'

But when it was time to start work on the album in earnest, her insecurities kicked into high gear.

'I cried before I went in the studio,' Stefani says. 'I was just terrified.' Writing songs with her band of 17 years seemed like a piece of cake compared with trying to be creative on cue, alongside Pharrell Williams or Andre 3000 or Dr Dre. 'It was very threatening to let these people into my world,' she says. 'Because that's what I define myself as - a songwriter. The hardest part was letting someone even suggest an idea and then my ego being able to take it if it was good.'

She got together with Perry, and on the first day they wrote a song called 'Fine By You' that didn't make it on to the album. 'It was all about: "I don't want to be inspired. I don't want to call anyone. I just want to sleep and wear the name you gave me. And everything I do is fine by you and you don't judge me and you love me,"' Stefani says. 'It was a stupid love song, but really good. I went home and felt good, like, "I did it. I wrote a song today." I was still scared to go back, and when I got there the next day, Linda had been sitting up writing all night. That whole jealousy happened - like, "You did that?"' The song Perry had written was 'What You Waiting For?'; it was her way of telling Stefani to get off her backside and stop complaining. 'It was like a dare, and I don't even remember writing the words,' Stefani says.

'I just barfed them out.'

Once Stefani felt comfortable with the direction of the album, her quirky creativity took over. She became fixated on the idea of dedicating a song to the wildly dressed Japanese women she had admired ever since her first visit to the Harajuku section of Tokyo in 1996. 'Everyone had this crazy personal style,' she says. 'The last couple of times I was there, it had evolved into all these different things like the Gothic Lolitas and girls with blonde hair and dark tans and high heels, like they were from Hollywood. I was working with Linda, and I did a shout-out to them: "Harajuku girls, you got the wicked style." That's when the dream started.'

The dream, that is, of having four Harajuku girls help promote her album. The girls, whom Stefani named 'Love', 'Angel', 'Music' and 'Baby', are actually professional dancers whose main job - other than performing onstage with Stefani - is to stand behind her and look cute. But the idea also evolved into a running theme on the album: not only did she write a song dedicated to them ('Harajuku Girls'), but two other songs on Love, Angel, Music, Baby reference the Japanese fashionistas. 'I was thinking about calling the album Stolen Goods,' she jokes. 'Or It Was Yours and Now It's Mine.'

Maybe one day, she says, after she's started her family, maybe she will make a 'real' solo album.

'I would love to learn to play something so I don't have to rely on someone to collaborate with,' she admits. 'I've written songs on guitar, but I don't play guitar good enough to be free. If I could play every chord? I could write a million songs if I had that.'

But how will she know when it's time to stop fighting the ticking in her head and start her family? For a moment she seems at a loss for words. 'I've been making a conscious effort not to think about the future,' she finally says. 'I'm lucky to not have a real job, to be able to express myself, be creative and be relevant. I don't know what I will be doing in 10 years. How old will I be? Forty-five. I don't want to think about it to be honest, because it's a waste of time. Tomorrow night I'll be in bed with my husband again and it will be really great. It's all about right now.'