Mickey Mouse celebrated his 60th birthday two days early Wednesday with balloons, a four-tiered cake and a jazz band party, where his tailless friends disclosed he's a contented bachelor and a closet Republican. ``I think he's been a Republican,'' said Roy Disney, who ought to know. No sooner had Walt Disney's nephew uttered the R-word than Michael Eisner, board chairman of Disney's $3 billion corporate empire, grabbed the microphone and said, ``No, he's non-partisan.'' But the elephant was out of the bag, and Mickey didn't deny it. Fat, sleek and eternally grinning, he merely bowed and waved a white-gloved hand at his adoring fans at the Smithsonian Institution's National Museum of American History. It was 60 years ago Friday, on Nov. 18, 1928, at the Colony Theater in New York City, that Mickey made his film debut in ``Steamboat Willie,'' the first synchronized sound cartoon in black and white. To mark the anniversary, museum director Roger Kennedy was given six original pencil drawings of Mickey Mouse sketched by Disney's chief animator, Ub Iwerks, for ``Steamboat Willie,'' along with a replica of an animation cel, or celluloid painting, used in the film. Mickey also gave Kennedy a happy birthday T-shirt and a hug. The drawings and cel were put on display in the museum's collection of pop culture memorabilia, which also includes Archie Bunker's armchair, John Philip Sousa's baton and Dorothy's ruby red slippers. Kennedy said Mickey Mouse was ``a terribly important figure in American mythology,'' whose enormous worldwide popularity ``scared all those Wall Streeters'' who once rejected Disney's pleas for financial backing. Walt Disney, who died a multimillionaire in 1966, always said Mickey captivated the public because ``he's just a nice little guy,'' noted Roy Disney, a former Disney filmmaker who is corporate vice chairman. Mickey didn't seem to mind that Minnie, his ever-faithful girlfriend, had missed the party, even though tiny figures of the two cartoon mice topped the birthday cake. Does Mickey ever entertain thoughts of getting married and raising a family? ``He's only dating these days,'' Eisner said. ``At 60, it's too late for little mice.''