Michael Keaton delivers a remarkable performance — four of them, actually — in "Multiplicity." In fact, if ever there was a movie that showed off an actor's versatility, this is it.

One could argue that Eddie Murphy delivered a similar hat trick in "The Nutty Professor" — playing seven characters under heavy makeup — but aside from the lovable, overweight central role, they were merely cartoon sketches.

Keaton, on the other hand, uses no makeup and often has all of his characters onscreen at the same time, with only his body language, voice pitch, gestures and attitude to distinguish them. Yet each is so distinctive that there's never any doubt about which is which.

And, as anyone who has seen one of the TV ads knows, the special effects are absolutely amazing.

"Multiplicity" is a fantasy about a modern man in modern society who becomes so harried that he wishes he could be more than one person. But, as the saying goes, be careful what you wish for. . . .

Keaton plays construction worker Doug Kinney, who has a loving wife (the always appealing Andie MacDowell) and two adorable kids. He wants to succeed both professionally and domestically, but the pressures of his work and trying to keep up with family activities is getting him down. And his wife wants to go back to work, which means he has to help out more at home.

When a geneticist (Harris Yulin) offers to clone him, Doug is at first rather skeptical. "You Xerox people," he says incredulously. But once he's convinced, he leaps at the opportunity.

At first, Doug 2 seems like a great idea, a more aggressive representation of Doug's macho side, and a workaholic, handily taking care of business — and then some.

But Doug isn't crazy about being a househusband, so he gets a second clone, Doug 3, who embodies his more feminine attributes — he loves to take care of the kids, cook and generally run the household.

Eventually, however, Doug 2 and Doug 3 begin to feel harried, so they get another clone, Doug 4. But you know how a copy of a copy is never as good as the original? Doug 4 makes Forrest Gump look like Einstein.

Director Harold Ramis ("Ground-hog Day") manages to balance all of this quite well, and it must have been a challenge to choreograph scenes with Keaton playing two or three or four versions of himself all on camera at once.

But it's apparent that the four screenwriters did not spend nearly as much time on the script, which should have been a lot sharper, wittier and faster.

As it is, this is a one-joke movie that too often sinks in sentiment and is surprisingly sluggish in places. (There are also moments that may remind you of Keaton's "Mr. Mom.") Worse, at an hour and 50 minutes it's way too long.

On the other hand, when "Multiplicity" is funny, it's a riot. Thankfully, the big laugh sequences and Keaton's varied performances give the film a tremendous lift.

In all, this is a flawed but frequently hilarious special-effects farce and there are moments when you could swear Keaton had to be cloned to pull it off.

"Multiplicity" is rated PG-13 for sex — a sequence that is awfully explicit for the rating here — profanity, vulgarity and violence.