Once, when we were restless here at the SCANNER compound, we rented a bus and went en masse into New York to see the musical "Cats," which featured a bunch of actors running around in KISS makeup. Afterward, we scratched our heads mightily. "What's the big deal?" we asked ourselves. "Why has this show become the world's longest-running musical? If Andrew Lloyd Webber was going to make a musical from poems by T.S. Eliot, why didn't he do 'The Waste Land on Broadway'?" But what do we know? "Cats" is the world's most popular musical. And this week comes another hallmark: The first "Cats" film, supervised by Andrew Lloyd Webber himself, and its debut on television, Monday evening on Channel 13. On the next page, drama writer Peter Filichia has the story, including an interview with Elaine Page, one of the original stars of the musical. Before we go, be award that the results of "That '70s Quiz" can be found in Sunday's Spotlight section. Yours in TV, STEVE HEDGPETH