"Jaws 3-D," now at area theaters, makes a conclusive case for terminating further sequels to "Jaws," as if one were needed. It also reinforces the impression that 3-D is unlikely to make a sustained comeback until its optical inconveniences and dependence on hokey scare effects can be overcome.

When you balance those cardboard polarizing glasses on your nose and try to establish a focus on the screen, both the size of the image and the level of illumination seem drastically reduced. The viewing experience resembles watching movies through a nickelodeon.

As for plot, Mike Brody, played by Dennis Quaid, is supposed to be the engineer responsible for designing a new Sea World attraction, a complex of underwater tunnels that permits customers to stroll around watching the marine life through plexiglass walls.

Quaid and Bess Armstrong, cast as the park's chief marine biologist, are envisioned as a romantic-heroic match. Their stable affair supposedly faces a threat from job opportunities that may take them to distant parts of the globe, but before that crisis can be dealt with, they're obliged to cope with the threat posed by a Great White Shark that penetrates the park's defenses and begins feeding within the compound.

In the original "Jaws" the townspeople, but not the audience, were meant to breathe a sigh of relief at the capture of the wrong shark, always suspected of being a wrongie by the Richard Dreyfuss character. In this variation the audience and the marine-wise hero and heroine are supposed to be tricked into a sense of false security upon the capture of a Great White, little suspecting that there's a bigger, badder one still swimming around the park.

There are some shocking oversights in the aftermath of the attack sequences. Mike's kid brother Sean, played by John Putch, and the girl he's attracted to, a flirty water-skier played by Lea Thompson, are never heard from again after she's placed in an ambulance soon after having the shark chomp her leg. Lou Gossett Jr., who plays the park supervisor, seems to be swimming around trying to save a coworker after the ultimate attack, but they're never seen in the obligatory, reassuring resurfacing shot.

The downbeat shocker is the sight of a grouper's severed head floating in the watery foreground after the shark bites. As alarms go, this one is scarcely worth waking up for: Should a shark be begrudged an occasional fish dinner? However, it sets the pattern for the 3-D shock effects, which emphasize severed parts floating in the foreground. The 3-D tricks also include a spritz of serum in the eye from a hypodermic and a harpoon in the eye. There's an ambitiously defective attempt to go all the way inside the shark's mouth with a struggling victim, but the underwater murk tends to muffle the grisliness of it all. Perhaps the neatest 3-D shot was a little frog who seemed to hop from his rock into your lap. Of course, when that's more diverting than the big effects, it makes you wonder if the big effects have really justified their existence. JAWS 3-D

Directed by Joe Alves; screenplay by Richard Matheson and Carl Gottlieb; story by Guerdon Trueblood; director of photography, James A. Contner; edited by Randy Roberts; executive producers, Alan Landsburg and Howard Lipstone; produced by Rupert Hitzig. A Universal release. Running time: 97 minutes. Rated PG. THE CAST Mike Brody . . . . Dennis Quaid Kathryn Morgan . . . . Bess Armstrong Philip FitzRoyce . . . . Simon MacCorkindale Calvin Bouchard . . . . Louis Gossett Jr.