Although it's their first non-Western, "The Domino Principle," now at area theaters, maintains the grubby standard set by earlier movies co-starring Gene Hackman and Candice Bergen, a casting come-on the public found resistible in " The Hunting Party" and "Bite the Bullet." On this occasion the indifferent duo may be found struggling to get their histrionic choppers into a stale hunk of melodrama about a murky but oafish conspiracy to assassinate the President.

Writer Adam Kennedy accounts for the title, which sounds vaguely familiar but incorrect, to the best of his meager abilities in a speech entrusted to Richard Widmark, the sleekest conspirator, who has arranged to get Hackman out of prison to exploit his allegedly peerless marksmanship.

Hired gun Hackman asks if their little escapade, depicted as successful but clumsy, can be expected to cause "a big stink." With puzzling smugness Widmark replies, "The bigger the stink, the more there is to cover up, and if the man in charge starts to panic the dominoes begin to fall." This emigmatic mixed metaphor lost me somewhere, but then I'm accustomed to seeing the dominoes fall because the kids insist on knocking them over prematurely.

The problem with "The Domino Principle" may be traced to incompetent, expedient dramatization, enhanced immeasurably by Stanley Kramer's dogged, blockhead direction. One can't decide if the filmmakers are more interested in reaching a public or taking a tax loss. In addition to reuniting the uncharismatic team of Hackman and Bergen, "The Domino Principle" seems determined to duplicate the American box-office failure of "Executive Action" and "The Paralax View."

Kennedy appears to be the sort of writer who habitually mistakes copouts for clever plot twists. As a result, his plot ends up chasing its own tail into infinity. Hackman reveals that he didn't shoot the intended victim after all, whereupon Widmark reveals that they never trusted him anyway, so the killing was actually accomplished by two unseen assassins. The movie ends with Hackman in the sights of an unseen assassin, no doubt another decoy.

The circumstances following the assassination turn into an unintentional comedy of blunders. The murder helicopter ferrying Hackman is suddenly disabled by security men who were nowhere to be seen only an instant before when the assassination occured. The helicopter ditches in a creek, and one of the plotters tosses an explosive device inside before anyone can get a safe distance away. The resulting concussion ought to terminate the Caper right there, but the plotters make their getaway and then blow up getaway car No. 1 before switching to No. 2.

As his escape plane taxis down the runway, Hackman watches Widmark's car go boom. Naturally, by this time one expects the movie to end on a truly appropriate note of hilarity with Hackman's plane disappearing in the clouds followed by a big exposion. Unfortunately, it grinds on. Evidently carried away by the challenge of impersonating An Average Housewife with lines like "Well, you must want to talk now. I'll go in here and make some fresh coffee," Bergen affects a country twang and appears in a frumpy brunette wig. She has, indeed, succeeded in making herself plain, but couldn't anyone tell her that a plain Candy Bergen has no reason for being on the Screen at all? "The Domino Principle" is the third release of the new year packaged by Lord, formerly Sir, Lew Grade. Although Grade has American capital behind him - the First National Bank of Boston is a key investor - his attractions seem pretty oblivious of American tastes and susceptibilities. The basic ingredients of movies like "The Cassandra Crossing," "Voyage of the Damned" and "The Domino Principle" - lame plots, mediocre direction, wasted Big Name actors, slightly furtive anti-American sentiments - maybe more suitable for foreign exploitation