One of the many major flaws in the Sharon Stone thriller "Sliver" is that when the mystery is solved and we find out the identity of the killer, it is a genuine surprise . . . but it makes no sense.

Then there is a very abrupt, punchline ending that leaves the viewer feeling more like the picture has stopped than concluded.As it is, the real mystery is why this thriller is wrapped up in this manner. The behind-the-scenes answer is that the ending was randomly chosen from several written at the last minute by multimillion-dollar screenwriter Joe Eszterhas and selected by director Phillip Noyce.

The original ending, according to industry insiders, had Stone and the killer flying over a volcano at the film's conclusion, when the killer suddenly confesses his crimes. He then veers the aircraft into the volcano as the end credits roll, leaving the audience to decide whether they survive.

That ending still is foretold in the film, as a small piece of table sculpture meant to represent a volcano is explained to Stone. Why that scene remains in the film, because it once had obvious resonance for the ending but now means nothing, is another unsolved mystery.

Anyway, test audiences who watched the movie with its original ending apparently hated it. So, the decision was made to come up with a new ending. Eszterhas wrote eight new endings, two of which were filmed.

If that's not enough, this new ending now reveals a different killer than did the original - a random decision, it would seem, for the sake of surprise.

But that merely serves to point out what's wrong with "Sliver's" plotting from the first few frames, and by extension, what's wrong with a lot of modern thrillers. If the killer to be revealed at the end of the picture can be chosen so arbitrarily, then there can't be clues earlier in the film that might subtly tip off the audience.

In the case of "Sliver," the revealed killer has no real foundation or motivation for his crimes. In this picture it could be anybody, simply because all the characters are so poorly conceived.

For me, this isn't so much a mystery as it is merely a maze of confusion, a maze that cannot be resolved until some outside force (the filmmaker) cuts down a hedge to let the audience step out?

Agatha Christie and Alfred Hitchcock must be spinning in their graves.

- THE MOST INTRIGUING new credit to come on the scene in awhile is in the opening of "Cliffhanger." The screenplay is by Michael France and Sylvester Stallone, but before we see that, up comes "Screen Story By Michael France." And before that, "Based on a Premise By John Long."

Based on a premise?

This brings to mind Danny Kaye's patter song "The Lobby Number," written by his wife Sylvia Fine, which he sang in his first film "Up in Arms."

The lyrics were about how long it takes for a modern (circa 1944) movie to get going, and Kaye sang, in part, this ode to a typical film's credits:

"Screenplay by Gluck

"From a stage play by Motz

"From a story by Blip

"From a chapter by Ronk

"From a sentence by Dokes

"From a comma by Stokes

"From an idea by Grokes

"Based on `Joe Miller's Jokes' "

It really is almost that silly.

- FOR ALL WHO have been asking (and you know who you are), Steven Spielberg's "Jurassic Park" finally has been rated by the Motion Picture Association of America's rating board - PG-13.

Considering how graphically violent the book is, a number of people have expressed concern that Spielberg's direction might be over the top in the gore department, earning the film an R. But he apparently held back.

Of course, you can get away with a fair amount of violence in PG-13 movies, so we'll reserve judgment.

The rating bulletin describes its reason for the rating this way:

"Rated PG-13 for intense science fiction terror."

Whatever that means.