For most actors, it's the sound of applause and laughter rippling through the audience that is the most gratifying. But for Stephen Spinella, it's the sound of gasps. The 37-year-old actor certainly incites his share of them as Prior Walter, the addled and flamboyant scion and reluctant prophet who is at the heart of "Angels in America," Tony Kushner's two-part epic about gays, AIDS and Reaganism.

The first murmurs of astonishment usually come from the Broadway audiences near the beginning of Part 1, "Millennium Approaches," when a naked Spinella, his skinny body covered with lesions, cowers and screams in terror. Another shock wave hits the audience early in Part 2, "Perestroika," when after tearing around the stage at full tilt, the ailing Prior falls backward in a dead faint.

"I can hear the gasps and then they're completely quiet," Spinella says. "They think it's some horrible mistake. Or that something truly horrible has happened. Which is where you want them."

Horrible things, of course, do happen in "Angels in America." But that horror is as often as not followed by something funny, provocative, malevolent or surreal. Prior is the lodestar for the play's amazing emotional journey, and the shy Spinella has emerged from relative obscurity to share in the honors that have been heaped on the hit drama.

"Angels in America" is divided into two 3 1/2-hour plays--Part 1, "Millennium Approaches," opened on Broadway in May, 1993; "Perestroika" followed in November and has been playing in repertory with "Millennium" at the Walter Kerr Theatre. The Broadway shows followed productions of both parts in Los Angeles at the Mark Taper Forum in late 1992, and "Millennium Approaches" was also seen in London earlier that year.

A year ago, when "Millennium" swept the Tonys-- taking, among its four awards, one for best play--Spinella took home the trophy for best featured actor in a drama. Now, with "Perestroika" again leading the Tony nominees for drama with six nominations, Spinella is up for best performance by a leading actor in a play. The change in category recognizes his role in Part 2 as more pivotal to the story line.

Whether he will prevail again when the awards are announced June 12 remains to be seen. He's got stiff competition: Sam Waterston ("Abe Lincoln in Illinois"), Christopher Plummer ("No Man's Land") and Brian Bedford ("Timon of Athens"). But whatever the outcome, Spinella says that he's bound to enjoy this year's competition a lot more than last year.