The writer's last resort is to write about the problems of writing. A novel about a novelist who is having problems writing a novel, or a film about filmmakers trying to make a film, or a newspaper column about the columnist's search for a column topic, are just about guaranteed to be the pits. And yet Ira Levin's "Deathtrap," a murder-thriller about the writer of murder- thrillers trying to think up a new murder- thriller and thus providing material for an apprentice writer of murder-thrillers who is trying . . . and so on, is in its fourth year on Broadway and now a star-cast movie. Even the play-within-the-play with which Jay Presson Allen's film version begins, shows actors portraying actors in a stage alley recreated on a stage recreated on a movie screen. "Deathtrap" is certainly one of the more clever arrangements of the mechanics of arranging things cleverly. It's like a Russian doll, where you're not surprised to find another doll inside, but can't help being amused when the tiniest doll still opens to reveal another doll, tinier still. It can be played either for the surprise or the amusement, and the film version, directed by Sidney Lumet, goes more for the laughs than the shrieks. Because the actors have gone for the outrageous and succeeded, it turns out -- after an opening that doesn't quite mesh -- to be very funny. There's Dyan Cannon as a wife with an anxiety level so high-pitched that her loving, supportive, wifely reassurances are enough to make anyone break out in hives; her husband complains that she screams every night at the sound of the door when he comes home. Michael Caine, who plays the husband, is all suavity with a ripple of nervousness underneath that one can see slowly swelling. Christopher Reeve, as the apprentice playwright, is the personification of flawless pragmatism. And Irene Worth, as a Dutch psychic who keeps appearing at dark windows, is beyond description. In such a crowd, the hope is not so much to discover whodunit, but to stave off the murders as long as possible. DEATHTRAP -- At the AMC Academy, AMC Skyline, K-B Georgetown Square, NTI Tysons Center, Old Town, Showcase Mercado, Showcase Turnpike, Springfield Mall and West End Circle.