MISSION, KAN. — A BIG wind greeted Buster Keaton's birth in the tiny farming community of Piqua, Kan., on Oct. 4, 1895: A cyclone leveled the tent of his father's traveling medicine show. The town of Iola, located six miles from Piqua, celebrates the windblown comedian's 100th birthday with its third annual Keaton Festival, from Sept. 29 to 30. Enthusiasts, fans, scholars, and preservationists will gather to honor the life and work of this preeminent Kansan. Keaton's face and body were metaphors - his impassive expression was the only implacable feature on a perpetually moving body. He was a poet of speed and also comedy's ultimate pragmatist. The consummate tinkerer, he was always looking under the hood, forever taking things apart - locomotives (''The General,'' 1926), prefabricated houses (''One Week,'' 1920), ocean liners (''The Navigator,'' 1924), even movie cameras (''The Cameraman,'' 1928). At once the credulous yokel and the canny sophisticate, he fell under the spell of corny medicine-show stage illusions - he was given his nickname ''Buster'' by magician Harry Houdini - and transformed them into the surreal events of ''Sherlock Jr.'' (1924) and ''Steamboat Bill Jr.'' (1928). Unlike Chaplin's sentimental Little Tramp and Harold Lloyd's breezy optimist, Keaton's character seems wholly modern in his blend of logic and lunacy. (Small wonder that intellectuals and artists from Jean-Paul Sartre to Samuel Beckett loved him.) Leaning into the wind, his hand shading his eyes from under the promontory of a hat brim, he gazed at the storms and machinery of a world forever in turmoil. Audiences began laughing at the poker-faced clown as soon as he stepped onto a stage at the age of three. By the time Buster was five, he was a fixture in his family's traveling show. At 21, he was making short films with one of America's beloved comedians, Fatty Arbuckle. Working independently in the decade of the 1920s, he made 19 short comedies and 11 feature films that placed him in the front rank of film comics, on a par with Harold Lloyd and Charlie Chaplin. Those were the peak years of Keaton's artistry and success, when he made $3,000 a week and lived in a magnificent house. But then, as abruptly as one of his pratfalls, things turned upside down. Surrendering his independence to the MGM studio factory system in 1928, he made a series of inferior films. Plagued by artistic restrictions and personal and financial problems, he found himself in the mid-1930s out of work, divorced, bankrupt, an alcoholic. It took 20 years to make his way back to the public spotlight - years in the trenches of MGM writing gags for Red Skelton, Lucille Ball, and Abbott & Costello, and making appearances in bit parts in films. Although he never recaptured the wealth and acclaim of his earlier days, he worked frequently on television (where he had his own variety show in the 1950s), made many successful advertisements for Esso and Ford, supervised the ''Buster Keaton Story'' (with Donald O'Connor in the title role) for Paramount in 1957, and enjoyed revivals of his work in Paris, Venice, Munich, and New York. Suddenly, everybody was talking about Buster. James Agee described him as a ''curious and original spirit'' possessed of a ''dreamlike beauty.'' The French critics went wild over his deadpan genius, calling him ''Malec'' - which means, ''the hole in the doughnut.'' He even received a standing ovation at the Venice Film Festival. ''Sure, it's great,'' he told film historian Lotte Eisner afterward, ''but it's all 30 years too late.'' He died on Feb. 1, 1966. In one of those tricks of perspective and illusion that he loved to play on audiences, the figure of Keaton has not diminished over time. Rather, its shape and enigma have grown larger.