"Nighthawks," an aggressively shallow police thriller pitting New York undercover cops against international terrorists, suggests what "The Day of the Jackal" might have looked like of filmed by the producers of "Baretta." In order to facilitate a grandstanding, harebrained heroic role assigned to Sylvester Stallone, the filmmakers brush off every opportunity for intelligent dramatization and authentic suspense that the plot would seem to possess.

Now at area theaters, "Nighthawks" appears to have a straightforward melodramatic game plan. The activities of the heroes, a pair of freelancing decoy copy played by Stallone and Billy Dee Williams, and the villians, a set of ruthless assassins played by Rutger Hauer and Persis Khambatta, are meant to run briskly along parallel tracks and then converge, indecisively at mid-passage and decisively at the denouement.

Unfortunatley, screenwriter David Shaber hasn't laid the sort of tracks that can support a clever or gripping vehicle. The rickety foundation might be finessed by swift, dynamic direction -- the sort of approach William Friedkin brought to "The French Connection" or Walter Hill to "The Warriors," an urban thriller Shaber also helped fabricate -- but newcomer Bruce Malmuth isn't agile enough. And the surprise payoff at the showdown, a trick that customers may be obliged to play along with if they hope to take anyhthing away from the night's entertainment, is fundamentally preposterous, an act no astute lawman could affort if placed in a do-or-die confrontation with an accomplished assassin.

The filmmakers seem to be preoccupied with exploiting New York locations for fleeting picturesque sensation. Stallone and Williams are introduced entrapping muggers on the streets of Brooklyn. When one of the felons takes to his heels, Stallone pursues him up the stairs and along the platform of an elevated station. At least this encounter gets somewhere. As a rule, the movie specializes in picturesque letdowns and wild-goose chases.

Hauer, a smugly expert fiend introduced planting a bomb in a London department store, arrives in New York with a new name and face, eager to cause a stir in America. When Stallone, detached to a special anti-terrorist unit, improbably recognizes his prey among the stroboscopic murk and tumult of the disco crowd at Xenon, he lets him get away (and, incidentally, shoot a few patrons) to set up a footrace through the construction site of the new crosstown subway. Swell tunnel, pointless chase.

In the climactic episode Hauer and accomplice Khambatta (the exotic beauty who debuted with a shaved noggin in "Star Trek") hijack the Roosevelt Island tram, hold the passengers hostage, kill one for kicks and make outrageous demands. However, it becomes apparent that the Roosevelt Island tram, whatever its exciting possibilities for filmmakers present and future, is a peculiarly confined, exposed and suspended setting in this case. Before anything decisive can happen, the tram has to come back and everyone has to transfer to a more flexible means of transportation, i.e., a bus. Meanwhile, tension leaks out of the situation with an almost audible hiss.

It shouldn't be too difficult to rationalize a movie thriller about policemen dedicated to apprehending a terrorist bomber. But "Nighthawks" is so sketchily written that Williams has no identity to speak of, apart from the disillusioning one of underemployed star keeping his hand in. Stallone, scowling behind a bohemian facade borrowed from Al Pacino in "Serpico," tends to be at an even greater disadvantage by being tossed the occasional frayed thread of motivation.

For example, his fleeting attempts to reconcile with Lindsay Wagner, cast in the token role of his estranged high-fashion wife, merely invite unanswered questions about how these two got together in the first place. And for want of authentic documentation about a peculiarly urgent form of police work, bogus hostility is whipped up between Stallone and Nigel Davenport, playing an Interpol agent who supervises indoctrination of the anti-terrorist unit.

Every 10 minutes or so Hauer (far and away the most effective performer in the movie, and sometimes wittily reminiscent of Kirk Douglas in his caddish, menacing salad days) chimes in with a bombing or murder, but there is Stallone giving Davenport a line of guff about refusing to use maximum force if he should encounter the culprit in public. It's an absurd, contrived dispute. Given the nature of the threat, neither the hero nor the filmmakers out to be wasting time with hypothetical nit-picking. Their job is to get the job done, and they've made extravagantly sloppy work of it.