The People of the United States v. Richard Nixon, a mildly entertaining courtroom drama, is having a brief preview run at the Supreme Court this week before moving across the street to bigger and better things in the House of Representative. James St. Clair stars as the slippery lawyer who tries to clear the path for executive dictatorship. Leon Jaworski is, for the first time in his life, cast in the role of the hero. I know how this one ends, but I won't tell you because I don't want to spoil the suspense.

The Threepenny Opera continues its smash run at the Loeb this week. Everyone who sees this production of Brecht's masterwork praises it, and about the only fault to be found with the whole show is that some of the actors aren't up to snuff as singers. So what? The Summer Rep has reportedly realized all the political potential of the play, and that alone is reason enough to go see it. Shows tonight thru Thursday begin at 8; for the next two days admission is $4.95, the price goes up a buck on Thursday.

Left Turn, one of the few political revues in the area, is performed by the Caravan Theater every Tuesday at 8:30. This troupe, which combines music and poetry with their skits, is always insightful and clever. An evening of relaxed and enjoyable entertainment.

Theater Two is previewing a "State's Version" of Sweet Eros, the controversial avant garde play which was busted several times for "open and gross lewdness," tonight and tomorrow at 8. What hath the state wrought?

War Babies, the New York Theater Company's improvisional group, will perform tomorrow evening at 8 p.m. in Longfellow Hall for free. The group's visit to Cambridge is sponsored by a Vis Stud video workshop; a rare treat that's not to be missed.

The Tempest, part of a repertory offering that will alternate all summer with Oscar Wilde's Salome, is still in previews at the Public Theater on Soldiers Field Road in Allston. Remember the Public is an outdoor theater, so this could be a very pleasant way to spend a hot summer's night.