CIVIL CIRCUS -- At Trinity Theatre, 36th and O Streets NW, Wednesdays to Sundays through April 4. Tickets $7 and $8. For information and reservations: 333-4944.

Presidents and congressmen come and go, but Washington's Hexagon Club abides forever. Well, for 26 years anyway, which is how long the group has been putting on its annual spoof of life in Federal City.

This year's show is called "Civil Circus" and will run through April 4 at Georgetown's Trinity Theatre, give us a chance to laugh at our leaders and ourselves while benefiting the Kiwanis Children's Orthopedic Clinic.

One gets the feeling that this year's cast misses the Carter administration almost as much as Amy does, because anyone who sets out to satirize Ronnie Wrinkles has a tough row to hoe. And what can you do with a Cabinet whose most striking character is Alexander Haig, the balsa-wood soldier?

But the Hexagoners, a bubbly mix of professionals and amateurs, try hard and often succeed. A sequence on the implacable demons who randomly enforce the District parking irregulations most nearly strikes the tone the show tries for, which is gentle spoof rather than biting satire.

Topical humor is an evanescent thing; an otherwise effective hostage number suffers from the Ayatollah having let our people go too long ago, and Rita Jenrette bared all too late for her to become a character rather than a write-in. But then, come to think of it, it would be awful hard to top Rita's own act.

Such a show, written in spare time and rehearsed at night by people with demanding jobs, will necessarily by a somewhat hasty pudding lacking theme. But its weakness is also its strength, for one cannot help but enjoy watching a cast sparked by love of life and lampoonery. Even in dress rehearsal, with the inevitable missed cues and rough timing, it was solid good fun.

There are several knockout individual performances, especially Joan Cushing as a chatty Washington Society Lady and Julianne Martinez as Miss Piggy, and the Rockette-style chorus line is a real kick.