You don't have to believe in magic to believe in Jeff Cowan - but it helps. Cowan is a midget magician. A 13-year old, 5-foot eight-grader who performs (as his handbill testifies) a "program of modern mysteries . . . original feats in magic, sleight of hand and illusions. A never-to-be-forgotton event. Call Jeff for dates and rates." As they say in showbiz, the kid's a natural.

Cowan has played at school fairs and summer camps, but his specialty is birthday parties. The show is part magic, part cornball and the rest - chutzpah. "There are a lot of other kid magicians in Washington," Cowan said after a recent show, "but I'm the best." He had just spent nearly an hour entertaining a room full of six-years-olds, who screamed, laughed and tittered throughout.

"Moving right along . . ." he intones, extracting an egg from behind a boy's ear. Squeals erupt from the audience. He pulls out a skinny blue ballon and stretches it, bantering all the while. "Now how many of you kids have been to the zoo?" Silently, some hands go up. "How many have seen the elephants?" More hands. "Now listen," Cowan snaps, "you don't have to raise your hand. Just call out the answers. This isn't school, you know, this is FUN!" A smile beams from the professional's face. He puts the ballon to his mouth and blows so hard his cheeks turn crimson. With a few squeaky twists the ballon is turned into a poodle and given to a member of the audience. "Aaaaaah," the kids sigh.

For his next trick, Cowan asks the audiene for help. "We must all say the magic word," he says, "which in this case will be Lee-Ba." The words are a combination of the guest of honor's name (which happens to be Leo) and the word "birthday." "Now I want you to say Lee-Ba when I tap my magic wand," Cowan coaches. He dons a top hat, takes the wand and taps an empty box. The audience mutters the magic words softly and Cowan extracts a blue silk from the box. "You didn't say it loud enough," Cowan complains. So he taps the box again. This time the audience, including the grown-ups, chants "LEE-BA-LEE-BA-LEE-BA" as Cowan pulls one colored silk after another from the empty box and piles them on the card table. More squeals.

Cowan offers three shows in varying degrees of complexity - the $10 show (no balloons, no animal tricks), the $15 show (balloons, but no animal tricks) and the $20 show (the works). "My plan was that psychologically most people would choose the middle and take the $15 show."

He thinks there's a big boom in magic lately, but dismisses Doug Henning (creator of "The Magic Show") and other modern magicians as "not very original." Last year Cowan earned more than $100, money he put back into the show. He buys professional equipment and tests out new tricks at home. Has he ever run into any hecklers? "Well, yeah, there were a couple of sixth-graders at a school fair once. But I quieted them down."

There's something to be said for Cowan's style of entertainment. It's less professional, but also less patronizing than a similar show performed by an adult. The first Saturday of every month Jeff Cowan joins other magicians at Al's Magic Shop for a meeting of the "Junior Mystics of Washington." Prospective members are invited. But Cowan says he doesn't want to be a magician all his life. What then? He is packing up a wooden contraption after demonstrating his saw-the-lady-in-half trick.

"An avenging prosecutor," he says. "And crooks, you better watch out."