'Making films is like a boxing match...'

This job takes its toll,' Nicole Kidman murmurs, swathed in black, blonde hair drooping in the midday heat of a roasting hot day in Deauville, France, where her new film, Birth, has just been shown at the American Film Festival.

'This life I lead is a burn-out life. From cracked ribs [in Moulin Rouge] to freezing in Romania [Cold Mountain] and being emotionally stripped [Dogville]. You have to step away from it because you are required to give so much of yourself to do it well. I don't mind going to ground, though the media can sometimes make that difficult.'

She presumably means the public dissection of her divorce from Tom Cruise, her muchpublicised miscarriage, her supposed romances with Russell Crowe and Lenny Kravitz and the persistent rumours about her weight, as she is snapped at successive premieres looking pale and painfully thin.

Kidman, now 37, puts the latter down to hard work. Since divorcing Cruise in 2001 she has released eight movies, has one in post production (The Interpreter) and is in the middle of filming another (Bewitched).

'Making a film is like a boxing match,' she says. 'You have to take the punches and you can easily fall. I plan to slowly dwindle away, bring the train to a halt, when the time comes. I'm not sure when the resources are going to run out in terms of what I have to offer. I hate the interest in celebrities. In New York I go around without an "entourage". I walk quickly, with my hair pulled back, and make myself invisible. I go to the cinema with my kids just like anyone else.'

Still, it's doubtful whether Kidman will be taking Isabella, 12, and Connor, nine, to see Birth any time soon. A metaphysical love story directed by Jonathan Glazer (Sexy Beast), she plays a widow who believes a young boy is the reincarnation of her dead husband. Birth has drawn heated reaction, mainly for a controversial scene showing Kidman and the boy in the bath together. The suggestion that the encounter is somehow sexual has Kidman pulling herself up straight. 'There is absolutely no amorous attraction. I would never have done anything that I felt was exploitative. That would be disgusting, horrible. Connor is the same age as Cameron Bright, the boy in the film. That would revolt me.'

The subject of motherhood is much on her mind. She shares custody of Isabella and Connor, both adopted, with Cruise. 'It's interesting to raise kids as an actor because you set up home wherever you're working,' she says. 'It's crazy when you're all togged up in a glamorous costume and you're fixing a snack for the kids in your trailer or helping them with their homework. Now having kids and being single I tend to take one day at a time. As a single parent you do your best and hope it will be good enough, and you know something? Usually it is good enough.'

Despite her prolific output as an actress, Kidman has priorities. 'I don't like it when your professional identity becomes mixed up in the way people perceive you,' she says with sudden feeling. 'Look, I chose life before work. My children are the most important thing. Actually, we're going away on holiday now, to have a bit of an adventure together, away from the bright lights.'

Kidman has been in the bright lights since she played a sheep clad in car-seat covers in the school nativity play at the age of six and stole the show from baby Jesus. Her social activist parents - Mom was a feminist nursing instructor, Dad a biochemist and labour advocate - were encouraging of an ambition that even then seemed almost obsessive, allowing their daughter to drop out of high school to pursue acting full time. She left Sydney and cracked Hollywood in 1989 with Dead Calm. Tom Cruise caught the sea-faring thriller at a private screening in Beverly Hills and asked for the 'cute redhead' to be cast as his female lead in the Days Of Thunder. The rest, as they say, is history.

Kidman remains wary of discussing Cruise. Or is perhaps bored. But she will talk about Birth and playing a widow on the verge of remarrying. 'She is still captured by her belief in love, even 10 years later after her husband's death - I understand her.' Pause. 'I also have very strong things that drive me and have kept me surviving through all sorts of things in the past. Part of my journey as an actor is that in each film I am in a different space in terms of my life and where I am at psychologically. I don't necessarily seek roles that expose me physically and psychologically. They somehow manage to find me, but I am willing to be exposed.'