IT'S BEEN 30 YEARS since Norman Bates first started killing people in "Psycho." And, after three decades, he's back at it again in the made-for-cable sequel "Psycho IV: The Beginning."

"Norman hasn't changed that much," says Anthony Perkins, the actor behind the killer. "He still has a bad side."Despite the killings, Perkins still has a soft spot in his heart for the role - and for the character.

"I do have affection for Norman as a person," Perkins said. "He does the best he can out of the diminished circumstances with which his personality stranded him and . . . Norman's childhood was a difficult and dramatic one."

Followers of the series get a chance to look into that childhood Saturday night when "Psycho IV" debuts on Showtime at 7 p.m.

Norman is once again a free man. He's even settled down and married his former psychiatrist. But when he hears a talk-radio broadcast about boys who kill their mothers, he can't help but call in - and announce that he plans to kill again.

Prompted by the talk-show host (CCH Pounder), Norman recounts the events that led him to become a killer. In a series of flashbacks, Olivia Hussey portrays Norman's mother and Henry Thomas ("E.T.") plays a young Norman - long before Janet Leigh checked into the Bates Motel and took a shower.

"It answers many of the questions we really wanted to know," Perkins said. "How come? How did it happen? Why did it happen? What were the tragic turns of events that made this story the way it is?"

For those of you who missed the first two sequels, 1983's "Psycho II" started off as an interesting addition to the original, only to degenerate into a bloody mess at the end. "Psycho III" in 1986 was pretty much a slasher film all the way through.

But you don't really need to have seen Part II, Part III or even Part I to see Part IV - which is more a "prequel" than a sequel.

"All you really have to know is that Norman once again got hauled off to the rubber Ramada and . . . he wanted to be either executed or locked away forever so that he would never hurt anyone again," Perkins said. "Because Norman is, at heart, a benevolent soul - with a dark side."

As a matter of fact, Showtime is airing the original "Psycho" after Part IV on Saturday at 8:35 p.m. The film has been "restored" and has an enhanced digital soundtrack, and, according to Showtime, this is the first time it's ever been seen uncut and unedited on television.

Perkins said "Psycho's" longevity comes as a complete surprise to him. He never expected the movie would be a hit, let alone that Norman Bates would become part of American culture.

According to Perkins, the original movie didn't cause quite the reaction Hitchcock was expecting.

"In the first picture they (the audience) laughed so hard Hitchcock was dismayed and wanted to take the film back and remix some of the dialogue scenes so they could be heard," he said. "They laughed almost throughout the picture.

Perkins, who was forever identified with Norman after the first movie, says he hasn't tired of the part.

"It is the Hamlet of horror roles, and you never quite get enough of playing Norman Bates," he said. "It's always interesting."

And while he once tried to escape the Norman Bates image, Perkins now revels in it.

"I think it's my favorite role . . . ," he said. "So many thousands of people have come up to me . . . and shared their experiences of seeing the films with me. It's always been with the greatest amount of pleasure that they've done so.

"They've told me stories about the dates they had with their future wives and they've told me stories about sneaking out of the bathroom window and seeing it against their parents orders . . . always with a feeling of having been entertained and having been taken in by the story and having a good time.

"Of course, I enjoy that."

After four installments, is this it for the saga of Norman Bates?

"You can't foresee past the sequel you're making," Perkins said. "If you foresee past you are implicitly telling your audience that you're not giving them your full shot."

Without giving away the ending, this might be the end for Norman. But then again, the door is open at least a crack for "Psycho V."