Inside, the congenial din has momentarily drowned out the rhythmic racket outside -- the latter from a pile driver at a construction site next door, as Pennsylvania Avenue's monumental makeover progresses through the unexpected mildness of a mid-January Saturday afternoon.

Inside, Donna Devereaux, manager of a Dupont Circle video store -- who today also constitutes the entire paid staff of the Public Interest Follies -- would like the attention of the two dozen Follies cast and crew members gathered for a semi-dress-rehearsal. "I have an announcement!" she hollers.

Before anyone can fully respond, Follies veteran Suzy Robson -- a General Services Administration procurement analyst, dressed today in privately procured black Danskins and pink skirt -- puts her fingers to her mouth and whistles.

It is the kind of whistle you might use to summon farm dogs to dinner. Robson grins, sheepish but victorious; the rented Seventh Street dance studio is now so quiet you could hear a pin drop.

What you hear, however, is the pile driver.

Klaing, pause. Klaing, pause. All afternoon.

And it's to this hydraulic hammer-beat of capital improvement that this band of dedicated, theatrically aware liberals pound out their own idea of capital improvement: the eighth annual version of a passionate, politically aware satirical revue known as the Public Interest Follies.

As you may hear from those who've seen such previous incarnations as "La Cage Aux Public Interest Follies" (1984) and the "Counter Inaugural Balls" (1981 and 1985), the Follies is a refreshingly cold shower -- which rains mostly on the Reagan parade. The Follies is pointed, but it's also self-parodying. And it is funny.

But it's also a lot of work.

"Last night it was awful," whispers Ligeia Fontaine, energy consultant and writer, to a fellow producer during a run-through of a full-blown production number called the "Star Wars Can Can." Evidently thinking of the previous night's rough time, she bites her lip and frets in the direction of a somewhat synchronized chorus line. "Two of these people have never been here before."

After three more practice runs, though, Fontaine -- who wrote and produced the number, with help from Offenbach -- is encouraged. And it's a good thing: The 1986 Public Interest Follies, subtitled "Back to the Present," will go on tomorrow through Sunday at GWU's Marvin Center Theatre.

"It's a miracle we ever get it together," says Byron Kennard, a soft-spoken, 48-year-old community organizer, self-described "semiretired do-gooder" and author who founded the Follies, with environmentalist Peter Harnik, in 1978. "But more than anything, it's an amateur thing -- in the best sense of the word: You do it for love."

Except for coordinator Devereaux -- who gets a laughable $1,000 stipend to shepherd props, people, posters and assorted paraphernalia into a real production -- the cast and crew members are in it totally for love.

No trifling motivation, mind you.

"It's hard for me to participate in, say, a demonstration -- because it's so grim and morose," Fontaine is saying to a visitor, after the cancan cast is dismissed. "I don't believe you win converts to your cause by being dark and grim and doom-saying. This is a happy song," she says, speaking of her antiwar Offenbach piece. "The cancan," she says, "is full of sexual vitality."

The visitor is scribbling furiously in a notebook.

"The energy that's left in liberalism," Fontaine says, "that's what the Follies is about."

Energy, fine. And, as Kennard says, it also ought to be funny.

Thus writer, producer and Follies vice president Robson is one of two dancers who must end the "Star Wars Can Can" number with a front-and-center cartwheel. Or sort of a cartwheel, at this point. "Aagh," she says, picking herself up off the floor as the cast applauds. "I think we should reconsider the decision not to get disability insurance."

Thus Dennis Bass, an administrator with the Center for Science in the Public Interest, sheds his stage-manager position briefly to appear in the spotlight -- in duly conservative drag, with purse, fake wig and his own real mustache, as the title character of a piece called "The Maggie Thatcher Workout." ("This next exercise should not be tried by anyone with an unstable government," he says in a British falsetto, jogging lethargically in place to a thumping Pointer Sisters beat. "It's called 'Crushing Striking Coal Miners.' ")

Thus, in an urgent midrehearsal plea for props, calls go out for: a large black feather boa, a "snow saucer" and, from cast member Steve Perlman: "A man's business suit, if anyone remotely my size has an old one they don't want. You won't get it back -- I need to cut the sleeves off." This is mostly because Perlman will play a Rocky-Rambo-Reagan character, nominated in this Follies to be the Republicans' 1988 presidential candidate. ("I'm in favor of world peace," he tells the press, "as long as our peace is bigger than the Soviets' peace.")

And thus, near the end of the rehearsal, in the first-ever run-through of this year's opening "Back to the Present" title skit, Kennard, playing himself, encounters a young visitor from the future played by Tim Doyle, a Virginia schoolteacher and part-time actor.

"Was the 'Follies' a hit?" Kennard wants to know.

"Was it a hit?" Doyle says. "Why, the show recharged the entire liberal community with newfound spirit, and they went out and eventually retook the White House . . ."

"Cut the crap," Kennard says. "How big a hit were we?"