Mad about the girls

Rosalind in As You Like It is the longest female part in Shakespeare, and once the character gets into the Forest of Arden and into male disguise, she acquires a freedom of emotional manoeuvre far greater than that of any of the other cross-dressed heroines in the canon. She has been called the "consciousness" of the comedy, a compliment that would never be paid to Viola in Twelfth Night, say, or Portia in The Merchant of Venice.

The androgynous focus of desire when in masculine mufti, she also offers the supreme instance in Shakespeare of the way that men should rely on the superior emotional intelligence of women. It's a plum role but clearly also a daunting one. In the courtship game that Rosalind, in her alias of Ganymede, plays with Orlando, she has somehow to be up to her neck in the scenario she stage-manages and at a critically perceptive remove from it.

Rising to the challenge of the part now is the gifted actress Helen McCrory, whose last Shakespearean role on the London stage was a smouldering Olivia aroused by the cross-dressed heroine in Sam Mendes's farewell staging of Twelfth Night at the Donmar Warehouse. Now it's her turn to wear the trousers and to stir ambiguous palpitations, in David Lan's new West End production of As You Like It. This relocates the proceedings to late-1940s France and features Sienna Miller, in her stage debut, as Celia, the cousin and close friend who disapproves of Rosalind's transvestite dalliance with Orlando until she is felled by a comparable coup de foudre. I met McCrory and Lan one evening after rehearsals to talk about the difficulties and the satisfactions of both the central role and the play.

The actress is shrewd, witty, disarmingly direct and possessed of the kind of emotional honesty that can cut through crap. "You know," she declared with a throaty laugh, "at 35, there's no point in me putting on gingham and skipping round with a smile on my face. We [she and Dominic West as Orlando] are playing them as our age."

Rosalind is a part that has been pushed to various extremes - the thigh-slapping principal boy who looks as if she's gone into Arden in search of a panto and the zealous feminist who gives the impression that she'd rather be in a consciousness-raising group with Celia than play wooing games with the hero. The effect is to make her seem pert and irritatingly on top of her benign subterfuge.

McCrory, by happy contrast, stresses the heroine's passionate struggle. "I think she's overwhelmed - constantly - and one of the reasons she wants to be a man is not just because the disguise will keep her from being murdered and allow her to travel to see her father. It also gives her some sense of control - of controlling feelings and situations like the men she's grown up with - one of the things she's never had an opportunity to do as a woman.

"And when she chivvies the other people in the forest, it's not because she's some bossy little madam. You know that, with her, it comes from the heart. All her wit rises up to protect her heart when she can't cope."

Peggy Aschroft, who had two successes as Rosalind (one when she 25, the other at 50), never much cared for the part - remarking that this heroine "does go on". But it's the reasons for her spirited loquacity that make it sympathetic. McCrory's perception accords with Hazlitt's beautiful comment on Rosalind that "her tongue runs the faster to conceal the pressure at her heart. She talks herself out of breath only to get deeper in love". "I know," says the McCrory, "that when I, Helen, start babbling, it's not because I'm feeling confident."

I have witnessed two superb portrayals. Adrian Lester brought his extraordinary emotional transparency to the role in Cheek by Jowl's celebrated all-male production of the early 1990s. The second was by Victoria Hamilton who, in Michael Grandage's 1999 Sheffield Crucible staging, depicted a young woman who was desperately improvising with Orlando in order to stop herself from drowning in devotion. You felt that even the mock-marriage was a spur-of-the-moment inspiration. The impetuosity and ardour were wonderfully touching and funny - and the production also made you appreciate the psychological strain on Rosalind.

Helen McCrory supports the idea that the heroine lives from hand to mouth as Ganymede, with no overall game plan, and that matters are resolved only "in the last beat of the play". As for the comedy's beginning, she emphasises that Rosalind and Orlando recognise each other as soulmates because they start off as such damaged beings - she as the daughter of the banished Duke, he as the abused younger brother of dastardly Oliver. "They're so unhappy; they're so brutalised; they're so angry; they both have this feeling of being unloved."

For David Lan, one of the questions the play asks is: "How do we live if the urge to love is caught up with feelings of anger?" The realistic love towards which the hero and heroine work is contrasted in the play with the simpler stock relationships of the pastoral genre. "The pastoral convention is very tricky," admits Lan, "because it was a cliché that Shakespeare was satirising, but it's not one to which we have access except perhaps as antiquated parody.

"Working with the designer Richard Hudson, I thought that what we need is to find another cliché - something that is immediately recognisable and about which there would be, as it were, no question."

Hence late-1940s France with its philosophers, its young post-war women finding a new confidence, and - with Arden set in the Ardennes - people who live very close to the earth. "The objective is just so that you can see the play. I am not trying to push a line. Part of the enchantment of the piece is that everything is many things at the same time. So the conceit of the design is that the forest is also the stage. The game is to try to keep the psychological reality of it but not to pin the play down, or it dies."

This co-production with Sonia Friedman looks like a canny package: class provided by the seasoned and stylishly astute McCrory; young bums on seats provided by Sienna Miller losing her stage virginity. Let's hope that, like Rosalind, the Young Vic manages to score a glittering success playing away from home.

'As You Like It', Wyndhams Theatre, London WC2 (0870 060 6633), 21 June to 3 September