Now that Congress is back in session, it's open season on politics and politicians. And this weekend you can pick your laughs from two barrels:

* For the past eight years, a group of working liberals have managed to escape their desks just long enough to put on the Public Interest Follies comedy revue. This year's program, "Back to the Present," will be staged three evenings this weekend at the Marvin Center, and includes such satirical spoofs as "The Maggie Thatcher Workout"; a Samurai warrior who takes on the deficit beast in "Gramm Kabuki Rudman"; and the "Star Wars Can-Can," a song-and-dance routine by Greek gods protesting the Strategic Defense Initiative. Last year this event sold out, so don't procrastinate. Tickets are $8 and available for Friday and Sunday only; both shows are at 7:30. Call 543-5097. The Marvin Center is at George Washington University, 21st and H streets NW. By Metrorail, exit from the Foggy Bottom station on the Orange/Blue lines.

* Veteran comic, syndicated columnist and resident Washingtonian Mark Russell comes home from the road for three days at Ford's Theater, 511 10th Street NW. Performances are Friday and Saturday at 7:30; Sunday at 3. Tickets are $18 and $20; seating is limited. Call 385-0044.