By Damian Fowler in New York

The play's cast includes Friends star Paul Rudd (l) and Bradley Cooper

It is a comeback of sorts for Roberts, who has not worked much in the last two years, excepting some voiceover work and a couple of animated films.

Instead, the 38-year-old film star has been devoting herself to her new family: her husband of four years and her 16-month-old twins.

It's hard to believe Roberts is a stage novice, but she is.

So why would a woman who can earn $20m (�11.1m) per film return to the stage instead of the screen?

"I think it's called professional challenge," says Leah Rozen, the film critic for People Magazine.

"There are those who are willing to do theatre and are willing to stretch their wings. And on the New York stage right now, she's queen of the city."

She's putting herself out there and she certainly doesn't need the money or the accolades John Breglio, Broadway producer

Three Days of Rain has become the hottest ticket in town.

Despite tickets costing up to $250 (�140), the show is sold out for its entire run, which ends on 18 June.

Every night after the show, for the past three weeks of previews, the pavements around the theatre are jammed with fans, eager to glimpse the star as she leaves the stage door.

"I admire her for putting herself on the line," says John Breglio, a Broadway producer. "She doesn't need to have herself reviewed. She's putting herself out there and she certainly doesn't need the money or the accolades."

Challenging role

"My family is very fulfilling and interesting to me," said Roberts, in a rare interview about her stage debut.

"And for me to step away from that for any period of time, I was going to have to do something that was really different and challenging."

Roberts won the best actress Oscar for Erin Brockovich in 2001

Three Days of Rain is a sensitive drama about three adults - a sister, a brother and a long-time friend - who, in the course of reading a will, unwittingly replay their parents' tangled relationships.

The play, first produced off-Broadway nearly ten years ago, is not necessarily the stuff that hits are made of. With its thorny dialogue and sombre characters, it is a far cry from current hits The Producers or Spamalot.

In the complex world of Broadway economics, it is crucial to have a big star headlining a revival like this.

Here, the gamble has certainly paid off. According to the League of American Theatres and Producers, the play earned almost $1m in its first week - unusual for a small play in a mid-sized 1,100 seat house.

Film stars have long been drawn to the Broadway stage.

In 1981, Elizabeth Taylor made her Broadway debut in The Little Foxes, for which she received a Tony nomination. In 1983, she made her second and last Broadway appearance, opposite Richard Burton, in Noel Coward's Private Lives.

Autograph-hunters wait for Roberts outside the New York theatre

In 1992, actress Jessica Lange, who had virtually no stage experience took on Blanche DuBois in A Streetcar Named Desire. Despite the fact the critics complained that her performance was too muted, she returned again last year in The Glass Menagerie.

"I think movie stars are lured by the legitimacy it gives them, and the very special glamour of Broadway," says Mr Breglio. "I'm sure they dream of winning a Tony. I think for actors that's the ultimate vindication."

This play is being seen as the beginning of a new phase of Roberts's career. When she finishes Three Days, she will go back to being a full-time mum. Then, in the autumn, she will film Charlie Wilson's War with Tom Hanks.

Whether the powerful New York theatre critics are cruel or kind to Julia Roberts, it is unlikely to affect her professionally given her megastar status.