"Nightwing" occupies some shaky but playable middle ground between "Prophecy" and "The Heretic." The rampaging vampire bats designed by Carlo Rambaldi to menace the humans in "Nightwing" are certainly more photogenic than the swamp monster who lumbers around "Prophecy." On the other hand, they fall short of the cockamamie symbolism of the locusts in "The Heretic."

Despite all the contrivances surrounding their invasion of the Southwest and threat to the populace, the bats have an advantage over both locusts and mutants - when finally sighted, they are more likely to spook an audience than give it giggles. They're not so esoteric that they transcend scariness. And they're effective litte devils: nippier descendants of Hitchcock's birds. It's the explanation for the invasion that invites confusion and ridicule.

"Nightwing" could lay a more justifiable claim to the little "Prophecy." We're supposed to share the final impression of the hero - a tribal policeman on an Indian reservation in New Mexico - who believes the vampires were summoned on a mission of vengeance by a tribal shaman who dies in the first reel and reappears in the last to complicate extermination plans.

Since the hero (played by Nick Mancuso) respects the old tribal beliefs, he is suspensefully torn between the extermination and letting the bats carry on the Supernatural One's holy war against the Anglos.

Despite his tribal loyalties, the hero is influenced by some strong medicine on the other side. His girlfriend, a high-minded Anglo who's been doing volunteer nursing on the reservation, is also on hand for the showdown in the cave of the bats.

He also feels responsible for the intrepid, fanatic bat exterminator who tracked the critters to their lair and now lies disabled and defenseless on the cavern floor. It's really no contest when you get right down to it, but the sources of conflict throughout "Nightwing" seem so arbitrary and elusive that it's not surprising to see suspense being fabricated at the last minute by sending the hero on an hallucinogenic bender in which the shaman mysticaly appears.

"Nightwing" is set against sharp-edged Southwestern scenery, but it never comes into focus as a horror melodrama. A tangible rather than mystic threat, the bats ought to simplify everyone's objectives and unify all the major characters - Mancuso as the stalwart Indian cop, Kathryn Harrold (sort of a second-string Jennifer O'Neill) as his girl, David Warner as the bat hunter and Stephen Macht as a young Indian politician with whom the hero frequently disagrees. Instead, all the subplots and petty rivalries only set up a racket that prevents the bats from assuming their rightful priority, like the shark in "Jaws."

It's a curious scare story that somehow contrives to shortchange terrifying situations as vivid as exploring a cave full of vampire bats shortly before nightfall or dangling from a rope over a pool of ammonia, the liquid waste of the resident bats. The mystical disgressions obscure such surefire perils. When the hero, who seems to be looking in vain for a father figure of some kind, starts debating right and wrong with the ghostly shaman, panicky impulses start to dissipate and can't be quickly reawakened.

"Nightwing" is too full of windy folkflore and peripheral conflict to suspend disbelief at the visceral level the premise justifies and the audience would probably prefer. CAPTION: Picture, Nick Mancuso struggles to save David Warner