"First Blood" is, one hopes, the last of the exploitation thrillers contrived to use the war in Vietnam as a rationale for gratuitous, sensationalistic eruptions of violence.

The Frankenstein's Monster formula revived in this defiantly outmoded new feature was reduced to knee-jerk cliche' by hack television dramatists several years ago. While the trend lasted, no TV action series could resist the cheap, self-congratulatory thrill of an episode in which a disturbed, misunderstood Vietnam vet went haywire.

The only theatrical features spawned by the same trend have been "Rolling Thunder" and "First Blood," an on-again, off-again project for about a decade. It might have remained mercifully off if fate had granted the eventual, unwary star, Sylvester Stallone, earlier opportunities to impersonate awesome warriors and/or psychotics.

The protagonist, John Rambo, is a brooding ex-Green Beret who becomes the scourge of small-town authorities who go out of their way to provoke him into striking back. The plot devices used to goad Rambo into devastating retaliation are shamelessly perfunctory and the characterization itself deliberately cryptic and inarticulate, right up to the moment Stallone permits himself a mawkish, blubbering curtain oration. Combining spectacular combat skills with stoical silence, Rambo seems at once superhuman and subhuman. The more appropriate titles have already been used, unfortunately: "The Savage Is Loose" and "Gorilla at Large."

Preoccupied and despondent after paying a visit to a buddy dying of cancer (apparently as a result of exposure to Agent Orange), Rambo is treated like a public enemy when he hikes into the small-town Oregon fiefdom of a fantastically hostile, stupid lawman, Sheriff Will Teasle, a regrettable no-win role for the usually winning character actor Brian Dennehy. The abiding motivational mystery of the script is what's eating Teasle and how the merely solitary, taciturn Rambo animates his ill-fated nasty streak.

Hassled on sight by the presumptuous sheriff, Rambo is arrested when he heads back toward town after being warned to stay away. Insulted and pushed around by the sheriff's subordinates, especially Jack Starrett as a sadistic deputy named Galt, the prisoner rebels, disables his captors with lightning karate blows and breaks out of jail, heading for the tall timber on a commandeered motorcycle with prowl cars in hot but ineffectual pursuit.

Beating the bushes for Rambo, the sheriff and his minions suffer one fatality and several gruesome injuries for their trouble. Strangely undaunted, even after Rambo spares his life when he has him by the throat, the sheriff persists in his feckless manhunt. Stranger still, this hideously blundering hick somehow ends up bossing a massive search party that includes elements of the National Guard and heaven knows how many other law enforcement outfits he couldn't conceivably have under his ludicrous authority in the real world. It's as if Wile E. Coyote had been given a division with which to ambush the Roadrunner.

And perhaps "First Blood" could only be enjoyed, in a sarcastic sort of way, if one regarded it as a mutant Roadrunner cartoon. Although the script is riddled with grotesquely laughable situations and lines -- poor Dennehy has to snarl corkers like, "I'm gonna get that psycho and pin his Congressional Medal of Honor on his liver," and, "I wanted to kill him so bad I could taste it" -- the nature of the violence is much too wanton and graphic to justify a carefree, humorously detached perspective. For all practical purposes, the story seems to end after about half an hour, when Stallone's character first eludes his pursuers and Richard Crenna, cast as Rambo's old commanding officer, enters to rile the sheriff by pointing out the obvious, i.e., he's out of his league and ought to fade gracefully out of the picture. Like the sheriff, the movie keeps functioning on sheer bloodyminded obstinacy.

The allure for Stallone, presumably, is the opportunity to combine soulfully suffering poses with an abundance of muscular physical exertion and assertion. The linkage is symbolized by the scars that crisscross his back and torso. For the purposes of the story, Viet Cong torturers put them there, but it's difficult not to perceive these scars as kinky decorative adornments to an already imposing star physique.

Stallone could barely restrain a smirk and a wink when making a spectacle of Rambo's toughness, particularly in a scene when he begins stitching up a knife wound on his bicep. Rambo isn't the role Stallone needs to free him from the successful yoke of Rocky. It's essentially a showoff stunt role, nothing but punishing, excruciating, outrageously exaggerated physical business in the survival-of-the-fittest vein. Turning to brute force without an underlying vulnerability and human interest, Stallone will probably find himself compelled to beat another hasty tactical retreat to the security of a "Rocky IV."