By JAN SJOSTROM, Daily News Arts Editor

Katharine Hepburn played some great roles. With Kate Mulgrew in the screen legend's skin, she becomes a great role. 

In Tea at Five, playing at The Cuillo Centre for the Arts in West Palm Beach, Mulgrew, known to Star Trek fans as Capt. Kathryn Janeway of the starship Voyager, looks and sounds a great deal like Hepburn. But the actress goes far beyond these inherent similarities, capturing Hepburn's peculiar quasi-English drawl, her up-tilted wide-mouthed smile, her ramrod carriage. She also gives a compelling interpretation of the inner Hepburn, a complex compound of vanity, self-deprecation, drive, scalding wit and vulnerability. 

The one-person format is problematic. It's difficult to establish a credible reason why characters are unburdening themselves to the audience or to develop a story line that sustains suspense. 

Playwright Matthew Lombardo dispenses with the first problem by offering no explanation for Hepburn's chattiness. As for suspense, he substitutes gradual revelations of the early experiences that scarred and shaped the star. 

The play is set in the living room of Hepburn's family estate in Old Saybrook, Conn. Act One takes place in 1938, when Hepburn, then 31, impatiently awaits word of whether she's landed a much coveted part she hopes will jump start her stalled career — Scarlett O'Hara. 

In Act Two, Hepburn is 76. Her best movies are behind her. Most of her friends are dead, including Spencer Tracy, the married man with whom she had a 27-year affair. 

Neither John Tillinger's direction nor Lombardo's script focus Act One, a series of anecdotes and one-liners strung together for no apparent purpose. It oddly ends with the arrival on Hepburn's doorstep of the script for The Philadelphia Story, a turning point in her career the show does nothing to develop. Instead of a through-line, the act offers scattershot biographical snippets and editorial comments that fill out the young Hepburn's cocky character. 

The best of these is her reading aloud a gossip column stating that she is in hiding after filming six flops in row. She crumples the newspaper and declares, "That's a downright lie. There were seven!" Mulgrew delivers the lines with perfect comic timing and a defiant flash of her eyes. 

In Act One, Hepburn roves the stage restlessly, flopping into chairs, curling up on a window seat, sprawling on the floor. Act Two's Hepburn is a radically different sight. Mulgrew's transformation is so complete that the audience burst into applause as the lights came up on her aged, Parkinson's disease-ravaged face. Act Two has greater dramatic unity and succeeds better in eliciting an emotional response. At the core is Hepburn's memory of her beloved older brother's suicide and her Yankee-patrician parents' repressed response to it. 

Hepburn's account of her 14-year-old self finding her brother's body hanging from a bedsheet is harrowing enough. Far more appalling is her subsequent attempt to win her father's approval by shaving her hair short, dying it blonde and dressing in her brother's clothes so that she would look like her dead sibling. Mulgrew's momentary disintegration after recounting this memory is riveting. 

Tea at Five is not outstanding theater. Mulgrew's performance is. The show runs through Jan. 25 at the Cuillo, 201 Clematis St., West Palm Beach. For tickets, call 835-9226.