The angel who appeared at the climactic curtain of "Angels in America, Part 1: Millennium Approaches" delivers her long-awaited message in Part 2, "Perestroika," which opened Monday at Signature Theatre. Like so many arrivals that follow a big buildup, it falls kind of flat.

The Signature production, directed by Lee Mikeska Gardner, is top-flight: There's so much good acting on one stage that it's almost dizzying. But Tony Kushner's epic "gay fantasia on national themes" runs out of steam as it chugs to a finish.

In her production of "Millennium Approaches" at the Signature earlier this summer, Gardner rescued the play from pretentiousness by anchoring it in the baffled lives of the characters. Her problem here is that the ratio of Kushner's windy and confused philosophizing to his witty, moving characterizations is too extreme.

Louis Ironson, who ran out on his lover, Prior, in Part 1, is still wonderfully acted by John Lescault, but he's been pushed to the sidelines. Joe Pitt (angry, affecting Paul Takacs), the sexually confused Mormon lawyer, is shunted by the playwright from failure to failure without our ever understanding quite what he's done wrong.

Joe's mother, Hannah (Marcia Gardner)--who, upon hearing her son was gay, sold her Salt Lake City house and came to Brooklyn--takes over much of the story. Matter-of-fact, tart and tough, she's a great character, and Gardner is great in the part, but she's come into the drama halfway through and remains essentially a supporting role placed by Kushner at center stage.

Joe's unhappy, Valium-addicted wife, Harper (bright-eyed, mad Melissa Flaim), wanders around being unhappy, just as she was in Part 1. Roy Cohn (Paul Morella), the demon-dybbuk who takes over the play by sheer strength of appalling personality, dies and takes most of the evening's energy with him. (In a peculiar choice for an edit, Cohn's flamboyant finale, in which he takes on the job of God's defense attorney, has been cut, denying both the character and Morella the exit they deserve.)

What we do have is lots and lots and lots of the Angel going on and on and on. Kimberly Schraf is authoritative, abrupt and funny in the role, but she's stuck with blather even Sarah Bernhardt couldn't have carried off.

God has abdicated, it seems, upset by all the change humanity is subject to, and the council of angels has decided to preach stasis. "Neither mingle nor multiply," the Angel tells Prior (Rick Hammerly), which, since Prior is gay, seems like somewhat misplaced advice. You'd think the Angel would be appearing in religious households and advocating birth control.

Though the Angel proposes stagnation, her approach brings on sexual ecstasy: If Kushner is making a point here, I continue to miss it, even after seeing the plays three times. Kushner does get a lot of comic mileage out of the shtick, though, and it's shtick Hammerly knows how to burnish so it looks like art. He's frightened, touching and dignified in his confrontation with the angels and, later, a total riot when, dressed rather like Death in "The Seventh Seal," he confronts Joe only to flee in panic ("He made me feel beyond nellie!").

The nurse Belize, who ends up with Cohn as his hospital patient, has more to do here, and that's all to the good. Craig Wallace plays Belize as deeply compassionate but nobody's fool. He can hold his own in the harrowing scenes with Morella's Cohn, then turn on a spiked heel and swish through a scene in a chic pink-and-aqua outfit, ironic, amused and, as he well knows, gorgeous.

Morella continues his stunning performance as Cohn. He looks like a ravaged bird of prey, and he plays the fading weakness of terminal illness with awful accuracy (this is the most convincing death from sickness I've ever seen onstage). Repellent but irresistibly vital, he makes the dying Cohn the most horribly alive person in the play. It's a shame he has to go out with a whimper instead of the bang Kushner wrote for him.

Once again, the designers have done superb work--from Ron Ursano's sound and original score to Lou Stancari's run-down set (like Cohn, it appears to be dying) to Michael Phillipi's lights, which pick out and isolate the actors' faces as if they were sculpted, to Anne Kennedy's costumes, which include such perfect details as a moth hole in Louis's sweater. There's not an element of the production that isn't top-notch.

Yet the evening still drags when the script goes flabby, and it goes flabby a lot. Beautifully done as it is, this is a long 3 1/2 hours in the theater.

Angels in America, Part 2: Perestroika, by Tony Kushner. Directed by Lee Mikeska Gardner. Props, Eleanor Gomberg. Assistant directors, Celeste Lawson, Holly Rudkin. Dramaturge, Gary Oiler. At Signature Theatre through Aug. 22. Call 703-218-6500.

CAPTION: Kimberly Schraf puts in a heavenly performance but her angel is long-winded in Tony Kushner's "Perestroika."

CAPTION: Paul Takacs, left, and Paul Morella in Signature Theatre's "Perestroika."