Even on a bad day, Cherry Jones radiates a generosity of spirit that is irresistible. That quality, combined with tremendous technical skills, has made her a consummate stage actor and a celebrated Broadway star. Now, after a long absence, she returns to her old stomping grounds at the American Repertory Theatre to tackle what just might be one of her more challenging assignments: the title role in Lysistrata, Aristophanes’s ribald comedy of 411 BC.

The challenge stems as much from the pressure-packed circumstances as from the role itself. Lysistrata marks Robert Brustein’s swan song as ART artistic director, and from the moment his final season was announced a year ago, it was clear that he wanted to go out with a bang. He invited Larry Gelbart, author of A Funny Thing Happened on the Way to the Forum (and at ART Mastergate and Power Failure), to create a freewheeling musical adaptation of Aristophanes’s ancient burlesque. Alan Menken (of Disney fame) and David Zippel would write the songs. Jones would star as the pacifist crusader who persuades the women of Greece to withhold sex from their soldier husbands until the men agree to sign a peace treaty. Andrei Serban, director of nine previous ART productions, would stage the comic spectacle, which would move on to the Prince Theater in Philadelphia following its Cambridge run.

But in February, in response to misgivings about the script by Jones, Serban, and scenic designer Michael Yeargan, Brustein rejected the Gelbart adaptation and decided to start from scratch, triggering a tempest-in-a-show-biz teapot. Weeks before rehearsals were to begin, Brustein set out to do the adaptation himself, with Galt MacDermot and Matty Selman scrambling to provide an 11th-hour score.

So as I speak with Cherry Jones, the final shape of this 2500-year-old play is still very much up in the air. " We are doing the impossible, " she says, as cheery as can be, despite being slowed by a nasty head cold. " We are trying to write a musical, on our feet, in four weeks. It is like summer stock, but with the added responsibility of having ART and Prince Theater audiences coming to see the final product. "

Jones points out that part of the challenge of adapting Lysistrata for a modern audience is that Athenian convention excluded women from the stage, so the play’s female characters were in effect drag roles. " You automatically shoot yourself in one foot by having women play these parts. The vulgarity that the women speak is tricky. If you go with men’s terminology for body parts with a man doing it, it would be hilarious. But in 2002 for a woman to use that exact same terminology is very tricky. Sometimes we have to figure out another way to make it incredibly vulgar, but from a feminine point of view, or it will be offputting. As a comedy, it has got to be charming. There has to be an innocence, and it has to be incredibly self-depreciating and at the same time self-empowering. You’ve got to cover so many different bases. "

In her career, Jones has covered many different bases — with tremendous success. As a founding ART company member (1980-’91), she played the title role in Major Barbara, Irina in Three Sisters, Viola in Twelfth Night, Grusha in The Caucasian Chalk Circle, and Cherestaní in The Serpent Woman, among many other roles. When she left the company to try her luck in New York, she achieved instant recognition: a Tony nomination for Our Country’s Good (1991) and an Obie Award for The Baltimore Waltz (1992). Then, in 1995, she won the Tony for best actress in the Broadway revival of The Heiress. She has been a marquee name ever since.

Jones’s success has not saved her from one of the actor’s occupational hazards: stage fright. " I have had this confidence crisis that has plagued me for three years now, I guess, " she admits, listing a number of contributing factors: encroaching middle age, the questioning of her own success, and a series of depressing roles back-to-back. Things reached a nadir when she took on the role of Josie Hogan in a Broadway production of A Moon for the Misbegotten, but she never missed a performance and went on to garner her third Tony nomination.

Still, returning home to the ART and taking on an unabashedly comic role is part of her effort to reclaim a sense of freedom and ease on stage. " This is such a lark. I can be sexy. I can be goofy. I can be an old yenta. I can be young. I can be whatever I need to be at the moment and decide what that is as I go. I have done so much grim theater for so long. I love hard theater, but it is just so nice for once to get to go to work where the object is to be stupid and funny and dear and innocent — and driven to save Greece. "

Lysistrata is presented by the American Repertory Theatre at the Loeb Drama Center May 10 through June 9. Tickets are $26 to $61; call (617) 547-8300.