In "Airport '77," the new installment of a series Univesal has threatened to continue for a generation, the writers simply give up trying to sustain airborne peril; they vary the formula by dropping a plane in ocean, so that it becomes a sunken airship.

Three blundering hijackers, including co-pilto Robert Foxworth; crash James Stewart's private luxury jumbo into the Bermuda triangle, where it settles precariously on a sandbar.

Awaking from a nap of knock-out gas, the poor passengers, a group of art patrons, journalists and hangers-on accompanying Stewart's collection of masterpieces to a museum dedication in Florida, find themselves battered and submerged.

The intrepid Lemmon succeeds in an ingenious stunt to escape the plane and reach the surface, where he sends a distress signal immediately picked up by his son Chris, cast a Navy radio operator. The climactic scenes concentrate on rescue operations conducted by Navy and Coast Guard personnel, who hasten to lift the plane with flotation collars before the fuselage caves in.

As the anonymous but admirably proficient sailors and divers go about their rescue tasks, "Airport '77" evolves into a recruiting film. There's a token attempt to keep the star on the scene by insisting that the frogmen need Lemmon underwater to tell them where to place the flotation collars, but this pretense is so flimsy one can't even resent it.

The finished film might as well be called "Coast Guard '77." The scenes so perfunctory and so poorly coordinated with the rescue operations for the purposes of creating and sustaining suspense that the picture loses even simpleminded melodramatic impact. The focus of interest becomes overwhelming documentary.

The filmmakers' conception of the audience may be measured by the fact that Jennings Lang, the Universal vice-president in charge of disaster melodramas, & Co. feel obliged to point out the obvious. The movie closes with a solemn assurance that while the story was fictional, the naval rescue techniques were authentic. If it's all the same to Hollywood, not everyone appreciates being addressed as a stupe.

In its resolutely dopey, arbitrary way, "Airport '77" is not without entertainment value. The faulty exposition and phantom characterizations are worth a few laughs, though the writers fail to generate the uproarious head of steam achieved in the recent TV movies "Mayday at 40,000" and "Death Flight SST."

Deploying Tom Sullivan as a blind piano bar player, who warbles a song called "Beauty Is In the Eyes of the Beholder," and Lee Grant as a shrewish drunk who scandalizes husband Christopher Lee and tries to walk off with submerged plane before being restrained by a Brenda vaccaro uppercut, earns "Airport '77" a little credit for incidental nuttiness.

Still, there's nothing in the movie-for-theaters to equal the dnouement of "Death Flight SST," where the stricken passengers voted to fly from Paris to Senegal without enough gas rather than put down in London and rather than put down in London and expose Europe to a nasty virus.

"Airport '77" specializes in a different kind of inconsistency. For example, millionaire art collector Stewart is given a token hostile daughter who sneers remarks like "My fathr is a very powerful man; he tends to dominate everyone around him." Meanwhile, good old undominating Stewart is behaving like a lamb and hurling threats like "W-well, isn't that w-wonderful?"

The movie gets a bit carried away with inside joking. Monica Lewis, the wife of Jennings Lang, appears as a stewardess who demonstrates MCA's new videodisc system, a jest calculated to back of on alert theater owners. Perhaps the most outrageous trick is stealing a joke from "The Big Bus": The only doctor on board turns out to be a vet. It's possible that the blind piano bar player is also back-handed trute to "The Big Bus," whose producers may console themselves with the thought that Universal has seen fit to crib what Paramount neglected to sell.