"Beyond the Poseidon Adventure," which opened yesterday at eight suburban theaters, is a damp microcosm. It tells the down-to-earth story of a dozen plain folks like you and me and Sally Field and Karl Malden, who come to terms with their life-adjustment problems while trying to find their way (through fire, flood and sporadic explosions) out of a sinkling, upside-down luxury liner somewhere in the mediterranean.

Sound familiar? Well, the ship is the same as in the original "Poseidon Adventure," and so are a lot of the incidental sloshing about and scaling of obstacles -- but this is a new script with a new cast, headed by Michael Caine as Mike Turner, a salty but lovable tugboat captain who needs some salvaged loot from the Poseidon to save himself from bankruptcy.

The time is a few hours after the last picture ended. Mike has just lost the cargo off his tug in a storm when he comes upon the Poseidon, abandoned and wallowing buttoms-up, its resplendent orange hull looking fresh from a studio paint shop and miraculously free of barnacles.

He is about to board it with his crew -- Karl Malden and Sally Field (who kind of wishes Mike would notice she is a woman) -- when up streams Telly Savalas in a motor launch with a sizeable crew. The arrival of Savalas is a historic event; he is a rat going aboard a sinking ship.

Only Telly knows it, but there is a shipment of plutonium down there in the cargo hold, and he means to have it for nefarious purposes that are not explained further. Savalas is posing as a doctor in search of survivors who may need help, so both crews go in together and, sure enough, they find a few passengers left over from the last picture. Then their exit route gets blocked.

You know what happens in that situation: The old facades begin to slip and we see people for what they really are -- cliches. We have a drunken fake millionaire (who turns out to be a pretty nice guy after all). There is a bigoted bully who Makes Up For It in the End. There are a pair of starcrossed young lovers and a touching older couple (he is a blind novelist, and they have stayed behind to die quietly together). There are tests of courage, endurance and compassion, a bit of gunplay and some diving, not to mention the kinds of weird scenery you expect from a sinking, upside-down luxury liner. When Mike and his gang get to the purser's office and its safe, there are surprises beyond imagining. The picture has everything except real people in real situations.

And were that not enough, Karl Malden is dying slowly of a mysterious, incurable disease.

The dialogue is carved out of antique wood. For example, this exchange between Caine and Field:

"Celeste -- I think you're beautiful."

"You do? (long pause) "You gonna kiss me?"

"No."

"Then let's get the hell out of here."

It is a sentiment that will be shared by many in the audience. CAPTION: Picture, Angela Cartwright, Jack Warden, Slim Pickens, Shirley Jones in "Beyond Poseidon"