Actress Kate Mulgrew is on a different sort of star trek in Tea at Five, the one-woman show in which she hauls film legend Katharine Hepburn from her Philadelphia Story incarnation to her lioness-in-winter one. Best known as Captain Kathryn Janeway of UPN’s Star Trek: Voyager (in which capacity, promoted to admiral, she has a cameo in the upcoming film Star Trek: Nemesis), Mulgrew used to resent the Hepburn comparisons that came her way. " This whole relationship between Katharine Hepburn and myself has certainly had its odyssey, " she says candidly (snapping out the movie queen’s name, as she does in the show, " Heppern " ). " For many years I never particularly liked her. I was compared to her so often that I began to resent that. The voice, there’s a little bit in the face, there are similarities. But it’s happened to me a lot in my life, and you begin to think, I’m Kate Mulgrew. But when I undertook this, not without some trepidation, it wasn’t long before I found myself falling in love with her. "

She’s not the only one. Matthew Lombardo’s Tea at Five debuted last winter at Hartford Stage, more or less in Connecticut native Hepburn’s back yard. From there it moved to the Cleveland Playhouse (in the state where Mulgrew’s husband, Tim Hagan, is campaigning for the Democratic gubernatorial nomination). The show begins a two-week Cambridge engagement, which will be hosted by the American Repertory Theatre, beginning September 8. Its hoped-for goal is Broadway, where no one is likely to say of Mulgrew, as Dorothy Parker famously did of Hepburn, that she runs the gamut of emotions from A to B. The actress’s portrayal of the much-imitated star ( " The calla lilies are in bloom again " ) is uncanny in its duplication of physical and vocal mannerisms but more than mimicry-deep.

As for the opportunity, it dropped into her lap. " It came to me serendipitously, as all good things in life do, " Mulgrew purrs through the phone from Cleveland. " My best friend knew a guy by the name of Matthew Lombardo. I had not encountered him over the 30 years of our friendship, so it was very strange that they had this close friendship I knew nothing about. Anyway, he was sitting with her one day. She just died of cancer, so they were lying on her bed watching an episode of Voyager, and he said, ‘You know, that woman has to play Hepburn.’ He went home and he wrote the play in three days. It was just one of those moments of alchemy. He put me together with her and a sort of magic took place in him. He sent it to me, in my trailer at Paramount, and I read it and I instantly understood that it was excellent. "

A virtuoso turn for Mulgrew, Tea at Five takes its name from what was apparently an inviolable ritual in the Hepburn home, where the tomboyish Kate grew up with a doctor father, suffragette mother, and a gaggle of siblings that included a beloved older brother who committed suicide as a teenager. (He hung himself, and it fell to the nascent movie star to cut the body down.) Lombardo sets the play at the Hepburns’ summer home in the Fenwick section of Old Saybrook, Connecticut (to which the subject, now 95, has retired). He fits most of 1938, when Hepburn was 31, into tea time of act one: the actress, having been recently declared " box-office poison " in Hollywood, is nonetheless lobbying by phone for the role of Scarlett O’Hara and being romanced by Howard Hughes. Before the cups are drained, she’s gearing up to see the family manse blown away by a hurricane.

Mulgrew explains that " Matthew has tinkered around with the first act, not insignificantly, since the Hartford run. He feels, and [director] John Tillinger and I agree, that we need to see more of Hepburn’s vulnerability in act one. Let’s see what drove her so hard. The curtain opens on this very agitated, feral cat pacing back and forth wondering whether or not her career is over. ‘Will she be saved by Scarlett O’Hara?’

" But of course all of that is only interesting in so much as it supports deeper feeling. And now, with this rewrite, we see that it’s not about Hollywood. It’s about who she saw herself as being, what she thought she needed to achieve in her life. It goes back to dad and mom, the suicide of her beloved brother Tom. She was 14 when she cut him down. This all defines the young Hepburn, whose adolescence was, to put it nicely, truncated. She was catapulted into a world of maturity, responsibility, and forced to accept the Hepburn mantle regarding grief, which was suppression.

" I think people who have a lot of suppressed grief are driven to excel in the world. Certainly she was. Her parents made no bones about it. ‘It’s one thing to be an actress, but you must be great, Kate.’ In Hepburn’s mind, this translated into movie stardom. Although she was no fool, which is why we still so admire and love her. Just as one would think she was about to walk the plank in Hollywood for the last time, she’d take off and do a tour of As You Like It. So she was always confounding, always a maverick; she was very complex. She defines herself as a kind of fascinating, spartan Yankee woman who says it like it is and says it very clearly. Well, that’s just the tip of the iceberg. "

Tea at Five’s second act once again finds us guests at Fenwick, but it’s now 1983. To start things off, the 76-year-old Hepburn, her hair a tangled gray upsweep, her leg in a cast following a car accident, shows us pieces of her mother’s tea service that have been dug up out of the sand following the 1938 hurricane that whistled in just before intermission. The 47-year-old Mulgrew reports that this limping, railing, reminiscing Hepburn is actually the easier to play. She says of her second-act turn, complete with cane, cast, Parkinson’s tremor, and recollections of Spencer Tracy: " It’s not so much bravura as kind of an uncanny, very lucky, natural fit, which happens, I think, when you get as intensely involved with a character as I have become with her. "

Indeed, Mulgrew watched all of Hepburn’s films in preparation for Tea at Five, read " every piece of literature I could find, " and has, to some extent, sacrificed her larynx on the altar of the part. In Hartford, some performances had to be cancelled because of the star’s vocal difficulties. But this, too, says Mulgrew, puts her in communion with the subject. " You know, Hepburn was always losing her voice, because she rode her vocal cords, and in order to affect this transition I have to do the same thing. Or shall I say I choose to do the same thing. I have to trick my voice. I travel about three octaves in this play. I’m very high and in my hard palette in act one, and then I go to the larynx in act two, and all of that within 10 minutes. I’ve worked with enough coaches, and they’re not all of the same mind. Some of them told me to forget it. But if I forget it, I lose the whole flavor of what takes me into her old age. "

About some Hepburn family members’ objections to the play, Mulgrew has this to say. " It was Katharine Houghton who rocked that boat, her niece [and the actress who played Hepburn’s daughter in the film Guess Who’s Coming to Dinner]. She loved her Aunt Kate and championed her cause and probably had every intention of writing the quintessential biography or of playing her herself as an older Kate Hepburn. She wrote a letter to the Hartford Courant. She was critical of the text but praised me. I think she just felt we had taken theatrical license. And we have — it’s a play. I’m sure they [the family] don’t want to discuss Tom’s suicide. They don’t want that Pandora’s Box opened. They have closed it so summarily. But this is her life. This is the story of what defined her as a young girl. And then the truth about her relationship with her father, which was less than pretty, evolving into this extraordinarily complex, one could even say diabolical, relationship with Spencer Tracy, to whom she was both lover and wet nurse. Dr. Hepburn was not what we would call a warm man but, boy, did she want his love. And that’s where I’m coming from in creating this. It’s all about love. "

And what about Hepburn on the screen, as opposed to Hepburn on the couch? " I think she got better and better, " says Mulgrew of the actress’s long film career. " But the thing she had, the thing that has caught fire, or certainly did in Hartford, she had true grit. She had real grit. You don’t see that anymore. She was fascinating because she believed she was fascinating. "

Mulgrew, of course, has a different kind of fanship, and Trekkies are more than welcome in the audience of Tea at Five. Having recently returned from communing with the faithful at a Star Trek convention in Las Vegas, the actress reports: " They’re not stupid. They’re quite bright, in fact, and they’ve been so supportive of this undertaking and have come, indeed, from all over the world. What could be more gratifying? When I say they’re not stupid, I mean to suggest that, actually, they’re quite devoted to the actor. They know that Janeway is just a character and that Kate Mulgrew is playing her. And what they are, first and foremost, is behind me as an actress, and they’ll come back and see it again, and those that haven’t seen it will come, and I suspect they will come from the nether regions of the world. "

Tea at Five will be presented by the American Repertory Theatre at the Loeb Drama Center September 8 through 22. Tickets are $32 to $62; call (617) 547-8300.