TAKE ONE ORDINARY BLACK UMBRELLA, a lamppost, a street full of inviting puddles and a patently fake studio downpour. Sprinkle with a lilting tune sung and danced by a guy who manages that rare combination of athletic grace and roguish appeal. The result is the most famous song and dance in movie history: the title number from Sing in' in the Rain, which marks its 40th anniversary this year with a new video containing footage cut from the original film. It features Debbie Reynolds singing "You Are My Lucky Star" to Gene Kelly.

Sitting on a paisley sofa in his white-shingled Beverly Hills house and nursing a stiff leg incurred during his hoofing days, Kelly, the man who both starred in and choreographed the exuberant rain dance, affectionately recalls its genesis. "I wanted to bring audiences back to their childhoods, when they would cavort in the rain even though their mothers would give them hell," says the 79-year-old actor-director. "[I also wanted] to make them feel like they were in love. A fellow in love does silly things."

Kelly knows whereof he speaks. Only last August the once divorced (from actress Betsy Blair) and once widowed (by the 1973 death of actress Jeanne Coyne) father of three married his third wife, television writer Patricia Ward, 36. The May-December lovers, who met in 1985 while working on a cable TV special about the Smithsonian Institution, are currently collaborating on Kelly's memoirs, to be published by Doubleday. "Everybody tells so many lies," he says. "I'm just going to tell the truth."

But not today. Abruptly brushing aside personal questions, Kelly wants only to talk dance. "It's a youthful thing," he says. "Doing it is a chore. Creating it is a joy." His legacy is such that even hip Hollywood pays homage. "He inspired me," says Paula Abdul, who based her dance with an animated cat in the video Opposites Attract on his pas de deux with Jerry the Mouse in Anchors Aweigh. Yet for the actor, who once flirted with the idea of producing a musical with Abdul as star, real life is now more pressing. Impatiently he looks at his watch. "OK, we're done," he says with a nod. "I've got a cocktail party to go to." Cheers, Gene.