Mickey Rooney was lounging quietly backstage, waiting for the curtain to go up on "Sugar Babies" during its recent run at the Warner Theater. Suddenly his voice rose, bouncing an echo off the walls of the small dressing room.

"How dare they!" he bellowed, challenging the right of the perpetrators of "Silent Night, Deadly Night" to co- exist on the planet. "I'm all for the first amendment, but . . . don't give me Santa Claus with a gun going to kill someone. The scum who made that movie should be run out of town."

And that was his reaction to just the TV commercial for the latest stalk-and- slash flick. Coincidentally he's offering an antidote -- or at least a psychic salve -- for the film that has been roundly criticized as desecrating a Christmas icon.he balm is called "It Came Upon the Midnight Clear" ("Shouldn't that be 'It Came Upon a Midnight Clear' wondered), airing at 8 Thursday on 5.

Rooney plays a retired policeman living with his family in California. He promises his grandson (Scott Grimes) a trip to New York to see what Christmas is like where Grandpa came from. He dies before the trip and has to strike a bargain with an angel (George Gaynes) to keep his end of the deal. Much to the surprise of the family, of course. Rooney and Grimes, finding no Christmas spirit in New York, set out to pump up the city. "It's a Frank Capra type of show," he said. "It's an old-fashioned Christmas tale.

"It was a perfect joy to make. It gave me a chance to work with Lloyd Nolan [who plays Rooney's parish priest] and, of course, Scott Grimes."

For Rooney, his appearance reinforces the idea that he has been a part of most phases of show business for longer than anyone can remembe "Sugar Babies" has become a staple of the American stage, he won an Emmy for his portrayal of "Bill," and his film career goes back nearly 60 years.

And he's not through yet. Rooney looks forward to playing Thomas Edison for PBS, and a Broadway version of "Maggie and Jiggs" is in the offing, with Carol Burnett. "Sounds kind of slick, doesn't it?"

But he's not looking forward to any more films. "I don't give a good tinker's damn if I don't make another picture," he said flatly. "There are only seven people allowed to make movies. Barbra Streisand . . . Burt Reynolds . . . Clint Eastwood . . . three or four others. But then we get into the awful pale of pornography. I'm not a prude. But we've really gotten out of control with our moral fiber. Our youngsters have been infected."

He'll do what he can to put things right with a fantasy-family offering for the holidays. "Christmas can be a mixed bag of nuts," he observed. "But for me it's always a joy. I'm a 64-year- old baldheaded kid waiting for Santa."