The Studio Theatre's revival of Harold Pinter's first full-length play, "The Birthday Party," starts slowly, but gets better with each of its three acts. Stay with it for a while, and this tale of intimidation and menace will end up sticking to you.

The last act, in fact, is as vivid and unsettling as anything the Studio has put on the stage for a long time. For the past 90 minutes or so, you see, two unidentified thugs have been psychologically brutalizing a one-time pianist named Stanley, the only customer in a shabby seaside boardinghouse. What he's done -- if anything -- we'll never know. But the interrogations have come to their end: Stanley is to be carried away in the sleek limousine purring just outside the battered screen door.

The thugs have dressed him up for the occasion, polished him to a near shine. Instead of the filthy pajamas he usually favors, Stanley is sporting a white shirt and a crisp, albeit ill-fitting, tuxedo with a pert bow tie. His flyaway hair has been slicked back and his face has been shaved of its three-day stubble. Three details, however, spoil the picture: He has a large purplish bruise on his forehead, a thin trickle of blood runs from his nose to his upper lip, and one lens of his glasses is smashed.

When he opens his mouth to talk, only strangulated garble comes out.

The moment is the perfect summation of a play that has lost little of its power to disturb in 27 years. Sardonically funny in places, as threatening as a thundercloud in others, "The Birthday Party" looks its age only when the thugs undertake an overtly absurdist grilling of their victim: ("When did you last wash up a cup?" "Is the number 846 possible or necessary?" "Why did the chicken cross the road?"). Innovative as such linguistic explosions were two decades ago, they sound old hat today.

Similarly, if "The Birthday Party" is no longer quite the bafflement it once appeared, it may be because Pinter has long since accustomed us to the opaque motivations and contradictory behavior of his characters, to the violence under the seemingly banal surface of life, to the irrationality of events and the human psyche. You can look at the play as a parable of political repression (especially in light of Pinter's most recent work), as a tawdry gangster story, as a Freudian dissection of guilt and atonement. But I'm not sure that's necessary. "The Birthday Party" is simply a play about an expulsion: A man, hiding out, is tracked down, pushed to a breakdown on his birthday and then carted away.

Call it Eden, if you want, or call it Brighton, as Pinter does. Interpretations are secondary. What counts is that the unexplained tensions still hold up in performance and that the climate of petty and cosmic dread continues to fill up a stage. In that respect, "The Birthday Party" remains as tantalizing a game of cat and rat as ever.

This is the watershed season that the Studio, operating under a special contract from Actors Equity, has begun the switch-over from the nonprofessional casts of the past to the fully professional casts of the future. You can sense the difference already. Such Equity performers as June Hansen and Harry A. Winter are right on the mark -- she as the maudlin old cow who runs the boardinghouse; he as the sleazy kingpin of Pinter's petty gang of two. (Winter suggests a kind of pathological self-control that is far scarier than outright anger.) Julie Frazer contributes a nice bit, as a tart who comes to the birthday celebration and ends up getting knocked around. And Joseph Scolero is the picture of British geezerdom, as the addled landlord who buries himself in the tabloids and his ritual bowl of morning cornflakes.

If elsewhere there's a slight falling off, it's not so drastic as to take the trouble out of a troubled evening. Robert Carroll, however, strikes me as too finely honed to do full justice to the role of the second strongarm. Where is the sheer lumpen menace of the character? And Morris J. Chalick, as the helpless birthday boy, could probably react to the proceedings with more of his gut and less of his mind. It's not until the drunken birthday celebration gets into full swing that he loses a lot of his self-conciousness and this eerie production really starts getting under your skin.

Using the sharp angles and distorted dimensions of a carnival fun house, set designer Michael Layton subtly announces the terror that will unfold in this run-down hovel. Daniel MacLean Wagner's evocative lighting manages to make even the sunlight streaming through the screen door look ominous and dirty, while costumer Jane Phelan spins telling variations on seediness and seedy elegance.

Under the hand of director Joy Zinoman, moreover, the production comes daringly close to pure expressionism -- emphasizing, as does the set, a fundamental sense of disproportion in human relationships. That may be the enduring fascination of "The Birthday Party." It is a mine field, and you're never sure who or what is going to set off the bombs.

As the mood thickens -- and it does at the Studio -- a toy drum becomes an object of terror. A mouth-to-mouth resuscitation seems to be an exchange of bodily poisons. And a lurching game of blindman's buff comes to symbolize all the brutal ways of an erratic and manipulative world.

The Birthday Party, by Harold Pinter. Directed by Joy Zinoman. Sets, Michael Layton; costumes, Jane Phelan; lighting, Daniel MacLean Wagner. With Joseph Scolero, June Hansen, Morris J. Chalick, Julie Frazer, Harry A. Winter, Robert Carroll. At the Studio Theatre through April 13.