You are my sunshine, my only sunshine . . ."

Chances are you're going to have to finish the verse before you read any further. There's a little machine in your head, mixing instinct and memory, that will propel the next few lines of this song regardless of whether you like it or not. "You Are My Sunshine" comes close to the perfect musical hook that one science fiction writer predicted could rule the world if it ever fell into the hands of a politician rather than a musician.

"You Are My Sunshine" is one of the great melodies of American music, kindergarten simplicity tempered by Tin Pan Alley craft. During World War II, when folksinger Pete Seeger was stationed on a Pacific island, he said that it "was a hit song among all the islanders and they all had a version in their own languages."

The song has been used as a lullaby, a courting song and a reinforcement against old age, a cradle-to-grave affirmation of warmth and love. It has been used to chase clouds away, to hold away the forces of nuclear power. It may have helped elect a governor, too.

The man who wrote the song, Jimmie Davis, was born in 1902 in the red clay hills of northern Louisiana, the eldest of 11 children in a sharecropper's family. Gospel and hillbilly music (as country was then called) were a major part of his upbringing. Starting his career as a Jimmie Rodgers imitator, Davis made his first recording in 1928 but he gave up the music business (reluctantly) as he pursued an academic career. When he was a professor of history and social science at Dodd College in the mid-'30s, Davis started to perform again. And then he wrote "You Are My Sunshine."

Though he could neither read nor write music, Davis (who will open the Smithsonian's Country Music series at Baird Auditorium Sunday night) was a prolific tunesmith. "A song's a very intangible thing," he says. "I recorded a lot of songs. Some of 'em I thought would be hits and nothing happened and some I thought nothing would happen and something did. Nobody can tell about a song."

The song became a big hit in 1938 and renewed itself as hit-material through such stars as Bing Crosby, the Andrews Sisters, Guy Lombardo and Gene Autry (who recorded many of Davis' songs). Having entered politics as a public service commissioner and criminal court clerk in Shreveport, Davis was convinced to run for governor of Louisiana in 1940. Campaigning with a combination of speechifying and singing, he won walking away, causing one disgruntled opponent to complain, "You can't fight Davis. How the devil can you fight a song?" Eddy Arnold, a long-time friend, rose to Davis' defense saying "he has a loyal following of fans, but more people vote for him than ever buy his records."

Once Davis and his matinee-idol good looks were ensconsed in an office, Hollywood came calling on the author of "You Are My Sunshine." The song became the centerpiece of "Louisiana," a Monogram bio on the singing governor (who had continued to make records on weekends). "I'd worked in other pictures, ridin' and shootin'," Davis says of films like "Frontier Fury" and "Riding Through Nevada." At home, there were protests about Davis' taking time off from public office to go to Hollywood and make films, so he turned down a sequel film called, appropriately, "The Singing Governor," and went back to running Louisiana.

Davis was elected to a second term as governor from 1960 to 1964, a time of racial turbulence that made him nationally known as a strict segregationist. When Ray Charles recorded "You Are My Sunshine," many papers called Davis, expecting the "hillbilly" governor to lash out. "The only thing I'm interested in is the fact that he did it," Davis said.

Despite his two terms in office, Davis never stopped writing songs or making records (though they were now mostly gospel). Among his better-known songs are the sacred "Someone to Care" and "Nobody's Darling But Mine" (which inspired Pasty Montana's hit "A Woman's Answer to Nobody's Darling" and "By the Grave of Nobody's Darling.") But "Sunshine" continues to be Davis' masterpiece. "I know I'm expected to do it," he says. "I'd rather go out and sing some of my new songs, but I found out that's a mistake. You sing the songs that people know you by."

In 1968, Davis' successor as governor, John McKeithen, vetoed a bill making "You Are My Sunshine" the official state song (claiming the lyrics don't mention Louisiana). Two years ago, however, Gov. Edwin W. Edwards officially made "Sunshine" the state song of Louisiana. "I appreciated it when they did," says the 79-year-old veteran of the twin twilights of politics and music.