SUPPOSE YOU WERE a once-successful but now faded dramatist and you wanted to write a classic Broadway thriller but didn't have any good ideas. Why not write a play about a once-successful but now faded dramatist who wants to write a classic Broadway thriller but doesn't have any good ideas? That's precisely what the protagonist in Ira Levin's new thriller, Deathtrap, decides to do and, not so coincidentally, it is what Ira Levin, a successful novelist (Rosemary's Baby, The Boys from Brazil) who hasn't had a Broadway hit in over a decade has done. Deathtrap economically combines two lastditch themes: the playwright-trying-to-write-a-play theme, which sets up worlds-within-worlds and all that twaddle, and the who-can-double-cross-whom-faster theme, the new nadir of the mystery genre, where all guns are filled with blanks, corpses fall to be later resurrected and everyone conspires against everyone else.

The drawing-room thriller once breathed haltingly in the hands of such skillful practitioners as Agatha Christie, but even ignoring its dubious dramatic value, the form was always limited. Having exhausted all possible realistic variations, it is not surprising that the thriller playwright has had to turn the form in on itself, self-consciousness being the last available twist. The character of Andrew Wyke, the bigoted, infantile, impotent detective novelist in Anthony Shaffer's Sleuth, was the logical culmination of the mystery-writer's view of himself in a world where such structured escapism has become frustratingly antiquated. It was an opportunistic out for Shaffer, himself a writer of second-rate mysteries, but Sleuth was both high comedy and a fairly stylish thriller, dumping on its own flailing genre with such viciousness as to end its death throes and lay it to rest.

Deathtrap is not the ingenious successor to Sleuth that Levin obviously wanted to write, but a desperate imitation of it. The same sorts of turn-arounds preponderate, and the playwright-protagonist, Sidney Bruhl (John Wood), as unscrupled as Wyke when it comes to murder, speaks in similarly sardonic conceits. But Levin, although he tries hard, has neither Shaffer's command of language nor his ability to make each epigram peculiarly illustrative of some aspect of character; Levin uses witticisms to fill pauses. To be fair, the script contains many very funny lines--assorted theater jokes, ESP jokes (one of the characters is psychic), a few bitchy asides that hit home--and the play succeeds more as a comedy than a thriller, but it is comedy of the most superficial kind. The last scene, which dissolves into a farcical exchange between the two characters left alive, is horribly executed, but suggests that Deathtrap has the makings of a clever, shallow spoof of greed.

The play's advertising representatives have asked the critics not to reveal the plot, but this seems rather silly--Deathtrap is tricky in a very predictable way. One has little chance to be confused: Bruhl constantly discusses the theatrical potential of the murders he commits, and ten lines rarely pass without a plot recap. It's rather like the old math problem about the frog in the slippery well who cannot jump three feet without falling back two. In addition, Levin makes his characters as self-conscious as his playwrighting. "Nothing recedes like success," quips Bruhl, and is so taken with the phrase that he writes it down for use by some character in his play (called, appropriately enough, Deathtrap). Outlining the plot, which follows closely the plot of the play we're watching, he concedes that the first scene will probably be "heavy and stilted," and when his colorless wife launches into a solemn, didactic monologue about why their marriage hasn't worked, he cuts her short with, "We get the gist of this passage." Well, we do get the gist of that passage, and the first scene is heavy and stilted, and all that this charming self-deprecation means is that Levin is a fairly good critic of his own work, although if he had been an excellent one he would have laid Deathtrap in a fireplace--the receptacle for so many drafts of the play-within-a-play.

The cast cannot redeem. Marian Seldes winces uncomfortably in her pointless role, and Richard Woods cannot enact a plodding, fatuous lawyer without giving a plodding, fatuous performance. Victor Garber coasts fairly pleasantly through his cunning young man role, and Marian Winters twinkles merrily as a psychic spinster, but we can't be allowed to laugh at her performance without another character reminding us that she is "the comedy relief."

John Wood, however, late of the Royal Shakespeare Company, gives a bravura performance as Bruhl; it's amazing what a little style, diction, and well-placed resonance can do even for a role like this. Wood resembles a jack-in-the-box out of the box, his long, gangling figure springing about beneath a jolly mop of brown hair. Best is his voice, which he uses like a virtuoso, rasping out some lines, snarling others like Burgess Meredith, or shooting up into a terribly British falsetto a la Rex Harrison. He conveys the tremendous nervous energy trapped inside him, which, unable to escape, manufactures a haggard lethargy; but here again the production seems unsettlingly close-to-life: Is it Simon Bruhl feverishly bored by the drying up of his creative juices, or John Wood feverishly bored by the obviousness of his role?

It's all a little too self-conscious to be much fun, and Robert Moore directs smoothly but without invention, serving the play rather than creating any visual stylishness. Deathtrap may have enough laughs to last a short time on Broadway, but as thrillers go, this one should be called Deathrattle.