The Threepenny Opera, premier production of the Harvard Summer School Repertory Theater's 1974 season, begins its first weekend of performances tonight and tomorrow. It's hard to imagine this professional production of the Bertolt Brecht classic being very bad. For the official line see Peter Shane's review which appears elsewhere in this issue. The curtain goes up at 8 p.m. tonight; tomorrow's show starts at 9. The Loeb is charging $5.95 a head for the weekend performances, so you may do well to wait for one of the cheaper weekday showings.

Kenyon Martin and the National Mime Theater begin their season at Lesley College's Welch Auditorium this evening and Saturday. The two-hour performance, reportedly the best the United States has to offer in this traditionally European art form, consists of a combination of classical mime and the company's original new piece, "Unnatural Acts." No jokes about how the show left me speechless. Tickets go for $3 a hit.

Anything Goes, a pretty good Cole Porter musical that's been produced a thousand and one times since the nostalgia craze began, premiers this weekend at the Washington St. Opera House in Sommerville. The 369 School for the Performing Arts, sponsors of the show, will serve meals at Saturday's and Sunday's performances. If the singing and dancing don't agree with you, maybe the bologna will. Call 628-0266 for more dope on this one.

The Great Molasses Flood of 1919 is, according to the press release, "an independent outerspace musical based on an actual event, with poetry by Joe Dunn, music by the Spheres and Carla Bee, and dance by Holly Whipple." It's not exactly clear what the actual event is, but in 1919 President Lowell sent Harvard students into Boston to scab during the police strike. Two students were killed while they did their class duty and undermined the workers. Maybe the molasses flood was more entertaining; it certainly must have been more heroic. The show is being presented by the People's Theater of Cambridge at 1253 Cambridge St. in Inman Square. Saturday's performance is at 8:30, two shows on Sunday at 5:30 and 8, one show Monday at 8. Tickets cost a buck and a half.

The Tempest, part of a repertory offering that will alternate all summer with Oscar Wilde's Salome, is still in previews at the Publick 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. Shows tonight through Sunday start at 8, admission costs $2.

Sweet Eros, a play by Terrence McNally, is still running at Theater Two near Kendall Square. This is Cambridge's current brush with the avant garde, so if you go in for that kind of thing you might as well see this before the U.S. Attorney follows his Boston act and closes this one down. It's playing with Michael McClure's The Beard, depicting the sexual confrontation between Billy the Kid and Jean Harlow. This could have been a lot better, but it's sort of cute. For the next two nights the performances begin at 8. Sunday's show begins at 7. There's a student rush.