Conquest of the Planet of the Apes. The fourth of the series of simian-centered fantasies. The time is 1991, and apes have become the new oppressed of the earth (though the humans shown don't seem much better off). Even the serial aspect is fun, though its also getting drawn out. Paul Dehn again has written a clever script, while J. Lee Thompson, who has become a bona fide yard-goods man, directs mechanically, at the SAXON.

Frenzy, A surprise from the supposedly declining Hitchcock. A virtuosic mix of suspense with apt characterization and subliminal social comment, set, thank God, in London, the director's home town. For once, the audience cheers when the hero doesn't kill his enemy. CINEMAS 57 II: 10, 12, 2, 4, 6, 8:10, 10:20. Fiddler on the Roof. The musical comedy, for all its shmaltz, was great, and the film is a faithful transcription. Norman Jewison directs competently, Oswald Morris's photography is breathtaking, and Topol's Tevye--virile and touching. CHERII THEATER. 2 and 8 p.m.

Fritz the Cat. An animated send-up of youth, U.S. culture, and things in general. Based, for the most part diligently, on R. Crumb's comic books, its pornography is irresistable, its funky satire entertaining on a very low level--making this a trap for snobs. ABBEY CINEMA I:1, 2:30 ,4, 5:30, 7, 8:30, 10.

The Graduate. Remember Simon and Garfunkel? Remember when loss of virginity was a fiery crucible for a young man's for woman's) character? Remember when you hoped that Mike Nichols would become a good filmmaker? Neither do I. PARIS CINEMA: 2, 4, 6, 8, 10.

Klute. Jane Fonda's Manhattan whore is one of the best female characters in American film, and one of the few honest modern ones. Don Sutherland's hick detective, a less difficult role, is just as well realized. The suspense story isn't much, but Alan J. Pakula's direction successfuly ignores it for long stretches. With Summer of 42, a well-filmed fable of initiation marred by a mawkish script. GARDEN CINEMA. Klute: 8 day, weekend matinee 4. Summer: 6:15 and 10 daily, weekend matinee 2.

Lawrence of Arabia. David Lean's best film. If the music is cliche and some of the post-release cutting execrable, Peter O'Toole's performance is classic--one of the few convincing portrayals of a man of genius in film history. The story is a guilt-ridden updating of the white man's burden myth, with sturdy construction and dialogue by Robert Bolt. HARVARD SQUARE THEATER, 2, 5:15, 8:30.

Paisan. Rosssellini's classic neo-realist film of post-World War II. Allied occupation of Italy. With Socrates, made by the Italian master for French TV (a Boston premiere). CENTRAL SQUARE CINEMA II. Paisan: 8:05, Socrates: 6, 10. Portnoy's Complainst. A vile reduction of the mythically pornographic Philip Roth novel about a successful Jewish lawyer and civil libertarian who couldn't help privately pulling his putz. Gone is the gloriously-guilt-ridden self-consciousness of the main character, replaced with the smirk of writer-producer-director Ernest Lehman. PI ALLEY, continuous every two hours from 10 to 10.

Slaughterhouse Five. Easier to accept than the book, because here Billy Pilgrim is the whole story. Uniformly well-acted, and though it won't shoot your pecker off, it won't leave you untouched. CHERI III THEATER: 1, 2:45, 4:30, 6:15, 8:10, 10:10.