On a bright green rug in St. Patrick's Episcopal Day School, masking tape indicates the size of the Trinity Theatre stage. A male chorus, some with canes, some using rulers instead, some holding invisible canes, shuffles through a soft-shoe while choreographer Ann Johnson revamps the staging, demonstrates a step, pulls and pushes them through their paces.

"Hey, you just walked through the wall!" one man shouts to another who dances over the tape.

Standing center stage, Tip O'Neill and Ronald Reagan (John Dow and Don Williams) quip their way through a vaudeville routine in a number titled "What Have We Got to Lose": "We're in our last terms -- we can say what we really think."

They're rehearsing for the 30th anniversary production of the Hexagon Show, the satirical revue that plays one month each year to continually sold-out houses. Spoofing bureaucracy, politics, Washingtonia and human foibles, the Hexagon Show runs on volunteer energy, tired muscles and creative brains, and each year the proceeds are donated to a different charity. Last year, with more than 20 performances following two months of evening rehearsals four nights a week, the show raised $130,000 for So Others Might Eat. This year's profits will go to the Columbia Lighthouse for the Blind.

Jim McKnight, a longtime Hexagon participant and this year's director, is among a handful of script writers and song writers who create an array of numbers from bawdy to ridiculous, generally causing hilarity by poking fun and occasionally throwing in a lyrical, gently mocking number to give respite from the belly laughs. "Hexagon is the only house in town where you can write original material and have it produced," says McKnight, who has written more than 90 songs and sketches, including "What Have We Got to Lose."

Jerry Breslow, with some 25 songs to his credit, has contributed this year's "Dole and Dole": "They'll run in '88, but will it be Dole and Dole or Dole and Dole?" Another Hexagon writer, Joan Cushing, has produced a paean to Hechinger's -- as the place to meet men. Doug Maurer has put together a salute to test-tube babies that sounds like a German beer hall song.

Contributions from other writers and collaboration with composers help to make the Hexagon a variety show. After a week's work in his spare time, Larry Heinen has completed the music for cast member Richard Schwartz's song about a creature who lives deep in the Metro caverns, damaging the Farecard machines and turnstiles -- the Metrognome.

Because this is an anniversary show, "we want it to be the best show yet," McKnight says. "We're using quite a few numbers from previous years," audience-approved favorites. "There's an oratorio that takes its text from a morning traffic report," he says, and a repeat of last year's outrageous "Hangar Club" routine, a send-up of one of the area's better known male strip joints.

Interspersed with the spoofs, local newscasters read off what sounds like real news -- until the punch line. "They have a lot of fun doing it," McKnight says. "It's the only time they hear anybody laugh at their lines."

Most in the cast have been in professional or community theater for years. Of 150 who auditioned, 60 were selected. "There are no novices," Strand says. "Most of these people are repeat Hexagon people. About 80 percent have done numerous Hexagon shows. A lot work for the Hexagoners, a group that performs for private parties year round to keep the Hexagon Show going."

The Hexagon Show opens tonight with 19 performances scheduled in Georgetown's Trinity Theatre, including an annual black-tie gala followed by a buffet. "This is going to be the million-dollar year," says John Maraney, public relations chairman. "We expect this show to put us over a million dollars in charitable contributions." The last number, he says, always a full-cast extravaganza, will express the sentiment "Thanks a Million."

The men doing the vaudeville routine leave the symbolic stage, making room for the next rehearsal -- five women who explain, "If a lady politician wants to be coequal with the men . . . we need sleaze!" In the next room a lusty chorus belts out the last of a jazzy tribute to Ballston.