If Clark Kent marries Lana Lang and Superman marries Lois Lane, will that be bigamy or menage a trois?

In "Superman III," with Christopher Reeve in the dual role, Clark gets engaged to Lana (Annette O'Toole), despite Superman's understanding with Lois. Then the Man of Steel's love life becomes even more complicated when he develops a split personality. A whiff of bogus kryptonite revs up his hormones and his heart smelts for the villainous lady Lorelei Ambrosia (Pamela Stephenson). "When she walks by," say writers David and Leslie Newman, "it's like watching the proverbial puppies playing in a sack." Oh, Superman, how could you?

Blame Richard Pryor who steals the show as Superman's lovable nemesis Gus Gorman, a computer genius who tries to destroy the superhero with a homemade kryptonite crystal. Superman, even though he's some 50 years old in comic-book terms, still doesn't recognize kryptonite when he sees it, so he handles the stuff and gets mean. He quits shaving. He blows out the Olympic torch and straightens the Leaning Tower of Pisa. We're talking vicious. And then -- and then, he crash lands in a junk yard and picks a fight with himself. Clark Kent sort of separates from the mean Superman and has it out with him. Good conquers evil and it's back to the storyline, as scrambled and unheroic a vehicle as ever challenged a superstar.

Reeve, five years after his first super film, is still still an incredible hunk and a treat for beef lovers. His red-headed costar O'Toole -- whose last big chance, a nude scene in "48 Hours," was edited out -- is twice as nice to look at as Margot Kidder (Lois). But O'Toole and Reeve don't ignite the way he and Kidder used to. Alas, the writers sent Lois packing to make room for the Smallville sweetheart.

Kidder plays two short scenes in the Daily Planet newsroom -- contrived to include "Superman" regulars Marc McClure as Jimmy, Jackie Cooper as Perry White and, of course, Lois, who goes on vacation and doesn't come back till the end of the film. She's the smart one for getting out of most of this madcap mishap.

But her costars struggle valiantly on as the tangled tale takes them from Smallville, U.S.A., to Colombia, where Gorman (Pryor, remember?), employed by crafty corporate creep Ross Webster (Robert Vaughan), has computer-generated a hurricane so Webster, his lover, Lorelei, and his mannish sister (Annie Ross) can corner the coffee market. Superman puts a stop to this pronto, but later, in his mean phase, helps the querulous quartet capture the global oil market.

When recovered, he clobbers Webster's ultimate weapon -- this summer's favorite felon: Mr. Microchips, a killer computer, who, as a suprise to nobody, turns on its masters and throws a terminal tantrum. Despite the final fireworks and special effects -- rather badly done at that -- it fizzles.

"Superman III" is high-flying disappointment. Looks like it's going to be an an endless summer of warmed-over leftovers. SUPERMAN III -- At area theaters. graphics/1 photo: SUPERMAN