Jean Shepherd Is a successful TV-radio personality, humorist and author. who's glad that he misspelled "scissors" at the age of 11 and lost the regional spelling bee In Hammond, Ind. "Defeat isn't pleasant ... he said, "but It's much better to experience It as a child than to have It happen for the first time at 30." Shepherd was reminiscing during a studio taping session of an interview for "The National Spelling Bee," whose finals will be aired for the first time tonight on Channel 20. The program will be produced by WKTA-TV, Washington, D.C., and presented on PBS through a grant from IBM. Shepherd. Who hosts the TV special. Finds spelling a fascinating subject. "It's a mystery," he said. "as to whether spelling Is an innate talent or a developed skill. Reading doesn't make a good speller - a great many bookworms and good writers can't spell at all. I learned to spell well by the fourth grade. In the seventh grade, I wound up in the regional finals of the spelling bee at Warren G. Harding Junior High School In my home town, Hammond. Ind. "I knew how to spell 'scissors' but I got psyched out by my opponent, a tall, cold-eyed fellow, who Is now one or Chicago's leading criminal lawyers. He never lost his cool. I did. And I never seriously competed again. Most losers follow the same pattern. Entering a spelling bee requires a willingness to be defeated. After all, you're bucking the elite, not the mainstream, in these events. It's a good thing to learn as a kid that there are always others more talented than you are. Shepherd. Who has had thousands of fans hanging on his every word since his offbeat nightly (except Mondays) musings began on New York's WOR in 1958, is also heard on NBC's weekend "Monitor" and daily on NBC's Emphasis." His show on WOR commands one of New York's biggest radio audiences and is taped for broadcast on stations throughout the country. It was Jean Shepherd's intense concern for correct spelling which led him to assume the host role on PBS' "National Spelling Bee," June 6. "When I receive fan letters from college students who write 'wood' for would and 'cood' for 'could,'" he said, "and, believe me, it took some doing to figure out the meaning of that second misspelled word. I feel a great urgency to impress the Importance of correct spelling on the nation's youth."