CATNIP FOR ANDREW LLOYD WEBBER FANS: In a production supervised by composer Andrew Lloyd Webber, "Cats" makes its world televsion premiere on PBS. by Peter Filichia Now "Cats" really is "now and forever." While the stage productions that have been playing in London since 1981 and on Broadway since 1982 have made that claim, those productions will close someday. "Cats", though, will now definitely live for time immemorial, thanks to a video version that's already in stores. And one that will be broadcast on Monday at 8 p.m. on Channel 13. Andrew Lloyd Webber's musical about the secret lives of felines has already been seen by 50 million people in 27 countries. But that will be a drop in the milk bowl compared to those who'll see this version, filmed on the stage of London's Adelphi Theatre. Not bad for a show that was given no chance when Lloyd Webber and producer Cameron Mackintosh first announced the project. A musical based on 14 T.S. Eliot poems? With human beings dressed in hairy costumes? With no real plot and just a lot of dancing? In a theater that had barely been booked for seven years? No, "Cats" had to be a dog. Things looked worse when Judi Dench, playing the hard-luck, bedraggled Grizabella, was hurt in rehearsals - experiencing the first of many back-wrenching, ankle-spraining, charley-horse inducing injuries that would befall thousands of "cats". To avoid a catastrophe, Lloyd Webber immediately turned to Elaine Paige, his original leading lady from "Evita". He knew that the woman who propelled "Don't Cry for me, Argentina" into a No. 1 hit could do the same for "Memory." "The very first time I ever heard ('Memory')," said Paige from her London home, "when Andrew played it for me at his house, I knew I was hearing a great song. Not only because it was a marvelous melody, but because it did something to me emotionally. I was desperate to sing it. I had an immediate passion - no, an obsession - to record it. Even after all this time, the melody still haunts me." So 17 years later, when Lloyd Webber asked Paige to reprise her role for the film version, she immediately said yes. "I didn't get to recreate Evita," she says a little testily, though without taking Madonna's name in vain, "so I was glad to recreate Grizabella." The actress saw the role through different cat's eyes this time out. "When you're 17 years older," she said, "you've had that many more life experiences. And because this is a cat who has lived, and suffered, and endured, I felt that I had grown into the role in a way that I couldn't have even envisioned back then." Nevertheless, Paige enjoyed the job more than she had in the past. "My problem with playing Grizabella in the London production was that I was always off-stage when everyone else is on. So I got very lonely just standing in the wings alone." With the stop-and-start nature of making a movie, though, Paige had plenty of opportunities to get to know her castmates. They include Ken Page, who played Old Deuteronomy, the fat-cat leader of the brood, in the original Broadway production. And then there was a significant new cat on the block: No less than Sir John Mills (an Oscar-winner for "Ryan's Daughter" as Gus, the old "theater cat" who ruminates how "the theater is not what it was." You can't prove that claim by Andrew Lloyd Webber, who went on to write the scores for "The Phantom of the Opera" and "Sunset Boulevard." For the acclaimed composer (on whom Queen Elizabeth last year bestowed the title of Lord) the filming of "Cats" in 1998 coincided with his 50th birthday. That was enough cause for a celebration held in Royal Albert Hall in London this past June. It, too, was preserved on a video that will broadcast early next year. In the meantime, now and forever, it will be "Cats", even more than the Energizer Bunny, that will keep going and going and going.