CAMBRIDGE - It is no secret why theater producers love one-person shows. Not only are they inexpensive, they are enormously popular with theatergoing audiences who come away thinking that they have actually spent time with a historical figure or a celebrity.

That is certainly the case with ''Tea at Five,'' Matthew Lombardo's play in which Kate Mulgrew seems to be channeling Katharine Hepburn. The American Repertory Theatre has imported the Hartford Stage production as a fall feel-good curtain-raiser for its own season of feel-not-so-good theater.

It is a remarkably calibrated performance by Mulgrew and, in fact, everything about ''Tea at Five'' is sturdily crafted. The two acts of the play are set in 1938 and 1983, and Jess Goldstein's dead-on costumes go from the elegantly casual white suit and heels to the plainly casual workshirt, turtleneck, and sweater of her later years. When Kate (H. or M., take your pick) falls into a chair on Tony Straiges's beautifully appointed Connecticut cottage of a set, they are so color-coordinated that she almost becomes one with the furniture.

But if imitation is the highest form of flattery, it is not the highest form of theater. The wait for ''Tea at Five'' to go much beyond People magazine recital of facts and pulling of heartstrings is not one that is well-rewarded in this two-hour journey, despite a wealth of material to draw from and the perfect actress for that material.

Mulgrew and director John Tillinger actually do go beyond imitation as the actress jumps around the cottage's living room in the first act as if she were training for the Athens Olympics, a perfect mix of tomboy spirit and Breck Girl appearance. Armed with a cane in the second act, Mulgrew gets everything from the self-assurance to the shakes right, although she does let an unwelcome bit of Carol Channing slip into the mix.

Lombardo is smart enough to make most of the names Hepburn mentions at both ends of her life somehow fit into the play. It seems at first as if Howard Hughes and Warren Beatty are mentioned only for the purpose of dropping names, but it turns out they actually become the punch lines for the first and second acts, respectively. In both acts Hepburn's career has taken a significant slide, the first due to several commercial failures (including ''Bringing Up Baby'') and the second because of Hollywood's disdain for older women. By structuring the play this way, Lombardo is poised to investigate how the real Katharine Hepburn drove the onscreen persona, but he seems too infatuated with the celluloid version to dig deeply enough into the former.

Intriguing questions just hang in the air without even a stab at an answer:

How could a woman so independent in the first act become so acquiescent to someone as abusive as Spencer Tracy in the second? Why do parents who seem like the lives of the party in the first act become such automatons in the second? How did her life affect her art? There are hints that we are in John Cheever territory here with closed-down and cloistered WASPs making Hepburn look for release in Hollywood, but Lombardo doesn't let those hints rise above an indecipherable whisper.

These considerations, frankly, did not seem to bother many others at Tuesday night's opening, which is perhaps another reason why producers love one-person shows. Audiences seem to demand less of the writing when there is a performance as good as Mulgrew's at the center.

My own measure of a one-person show like this is whether it makes you want to read more by or about an Emily Dickinson or hear more music by a George Gershwin. ''Tea at Five,'' unfortunately, does not take Hepburn to that level. If you're looking to rent ''The Philadelphia Story,'' you won't get any competition from me anytime soon.

© Copyright 2002 Globe Newspaper Company.