WHEN A MUSICAL like "A Chorus Line" comes to town, it doesn't slip in on little cat's feet. Not hardly. It arrives with all the pomp of an elephant-rich maharaja, bringing along all sorts of mental images and associations, and enormous psychological baggage train that the first-time viewer is stuck with, like it or not.

Inevitably, the show you see is not the one you thought you'd get. Not that there is any real problem with being bowled over by "A Chorus Lines's" brassy pizzazz, by being confronted with a show from which every scintilla of dead space has been ruthlessly removed, a show which is determined to entertain you to within an inch of your life. It's all rather nice, really, but it's not quite what I expected.

The surprise is how polished, how super-duper slick a production "A Chorus Line" turns out to be. "How charmingly naive," you may be thinking - but really, after hearing about the show, about what a "departure" it was, about how all these people were baring their souls and all, I expected something on the line of nitty-gritty gut spilling. Not "Oedipus Rex," but something a bit rough around the edges, something, shall we say, more hearfelt than calculated.

As it stands, "A Chorus Line" is very much a variation on the hoary backstage drama theme, a direct descendant of everything from "Stage Door" to "All About Eve." Once again, the boundless audience hunger to know what really goes on behind the scenes is played upon, once again we get a daring peek into the hopes, fears and yearnings of the little people, we get to live vicariously those exciting theatrical lives.

And "A Chorus Line" is extraordinarily deft in the way it gets you to feel for the dancers trying out, gets you to think its really you up there, wanting and needing that job, suffering and yearning for the main chance.

Yet somehow one has expected, one feels a need for more honest, sweaty emotion. "A Chorus Line" very cleverly lets you identify, but only to a certain point. It is touching, but not extensively; it hurts, but not enough to put a pall on your evening. If it wears its heart on its sleeve, it also outlines it in neon in case you might miss the point.

There are moments, especially in the story of Paul, a homosexual with a Puerto Rican background, when the emotion is quite real and affecting, but most of the time "A Chorus Line" seems to consciously avoid that kind of strain. All those months director Michael Bennett and the original cast spent working on the play must have been employed not so much in dredging deeply into the collective subconscious as in putting a high-gloss polish on a very sophisticated surface. It takes your breath away, but not your heart.

But having gone this far with "A Chorus Line," one should perhaps go a little further. Since in some ways this play is as good as theater gets, perhaps the problem is less with the show in a specific sense than with the general way theater operates.

Since theater is live, real people right in front of you, you inevitably expect a level of reality the medium does not appear to be equipped to give you. Instead you get "theatrical" effects. In fact the first thing you notice about "A Chorus Line," almost as soon as the curtain goes up, is that it is patently not real but an adroit counterfeiting, softening and rearranging of reality, a trompe l'oeil painting that however skillful and seamless can only increase your yearning for the real thing.

Ultimately, though theater may look real, its mannerisms and traditions make it more unreal, more distancing than a theoretically mechanical medium like film. One may have always known this, but it takes something like "A Chorus Line," with its earnest strivings toward verisimilitude, to emphasize the point.

To put it most baldly, we are somehow led to expect life - and we get a show.