Of course your kid is a Harry Potter fanatic. Of course she has read all three Harry Potter books. Knows all the characters by heart. Maybe she even insisted on waiting in line to get a book signed by Harry Potter's illustrious author in the Washington area yesterday. And yes, she really, really, wants to be Harry Potter for Halloween.

Like many parents you rush to the costume store and find . . . absolutely nothing.

No Harry Potter get-up, with his wizard's cloak, broomstick and taped-together glasses. No redheaded Ron Weasley or crooked-nosed Albus Dumbledore, smaller characters from the series. There are no costumes this year, despite the popularity of the Potter books by British author J.K. Rowling, despite the number of kids--and their parents--who read the books each night before bed.

Warner Bros. has bought the licensing rights to the books' characters, according to its spokeswoman. The company plans to issue its first merchandise next summer in the form of back-to-school supplies, Rowling says, and a movie is planned for the summer of 2001. But for now there are no action figures, no stickers, and alas, no costumes.

Think "Star Wars" without the giant cardboard cutouts of Jar Jar Binks. Think "Tarzan" without the commemorative plastic soda cups. Think Pokemon without the . . . Actually, no, that's unthinkable.

Which means that suddenly--gasp--a whole lot of parents are sewing. And remembering what a holiday once was.

Back in the days when mothers made the costumes, before Halloween went the way of packaged spiders and plastic pumpkins, before you saw yourself coming and going in your manufactured plastic Aquaman/Freddy Krueger/Power Rangers get-up, Halloween was about imagination.

Remember? The costumes were nothing complicated: A white sheet and eyeholes made a ghost; a black sheet, a witch; a red bandanna on the end of stick, a hobo. But in any case, you created, the way you put together your own model airplane and your own soapbox car.

Things have changed. Easier these days just to slip into a ready-made Pokemon suit. Which is why many parents looked high and low for the phantom Potter costumes. They phoned around. They combed the stores. They searched the Internet. And they were inevitably disappointed.

"The only site I found was a little boy in Florida who had made his own costume and wanted other kids to post their own," says Mary Lou Hartman of Chevy Chase, whose two daughters are dressing as Dumbledore and Ron this Halloween. "I was surprised. I felt sure that this would have been a tremendous marketing opportunity for someone."

But instead, as if regressing to an earlier time, Hartman and her daughters have become hunter-gatherers, searching out the crooked nose, the long silver wig, the half-moon glasses, the cape, the wizard's hat. But at some point their knowledge falls short and they are forced to rely on imagination. There are limited physical descriptions and few pictures in the Potter books, a fact that has given rise to some hearty debates.

Harry Potter's robes? "Black," one kid says, waiting in line outside Politics and Prose in Northwest Washington for a book signing yesterday. "Maroon robes, the last time I checked," says another.

Dumbledore's beard? "White." "Silver."

Hermione's eyes? "Light blue." "Green." "Hazel."

And as for the requisite broomsticks . . . My Harry Potter costume, says Bryan Stabbe, 9, of Potomac, will carry the "Fireball broom"--

"No! Nimbus Two Thousand!" shouts a little girl, referring to another kind of broomstick.

"I'm going to have a Fireball," Bryan says firmly.

Lizzi Bowers, 10, who lives near Paris, Va., would much sooner make her own costume with her mom than buy one. Of course, she's not the one sewing emerald green velvet with sequins into a cape. Nevertheless, there's an integrity to the original creation, Lizzi says.

She would never wear a Pokemon costume--something like that is "not your creation," she says. "It's just buying something else that someone else thought of. . . . It's like going out and buying someone else's ears."

Outside Politics and Prose, a group of kids circles a display of Pokemon cards while waiting for Rowling to appear. What do you think about a Harry Potter television show, just like Pokemon? What about a Harry Potter movie?

Several kids recoil--they wouldn't like that at all. No, no, that would change something.

"It just wouldn't be the same," says Ben Seydewitz, 10, of Wheaton.

"I don't think they should make TV shows because then when you imagine stuff from the book, then it will be much different," says Sam Piazza, 10, of Silver Spring.

Costume shop owners have mixed opinions about the dearth of Potter paraphernalia. On the one hand, they like the idea that kids have to make their own costumes, they say. Like the old days.

"On the other hand," says Barbara Posaner, the owner of Repeat Performance in Rockville, "having the pre-made costumes does sell 'em." Posaner has been selling costume pieces like capes and glasses, but thinks she would sell more of the manufactured ones. "Mothers don't stay home and make costumes anymore. . . . The imagination days are almost gone."

Harry Potter is not like Pokemon or the Power Rangers, says T.J. Pekin of Costumes Creative in Silver Spring, where a number of families have come to piece together a Potter costume. "There's no movie. There's no video game. It's not something that was designed to sell kids and make them buy something."

Well, at least not for now.

CAPTION: Lizzi Bowers designed her own costume. She's dressed as Hogwarts Professor McGonagall.

CAPTION: A Harry Potter Halloween: Sydney Bowers helps daughter Lizzi, 10, try on her homemade Professor McGonagall costume.