You can always tell the bad guy by the hat he wears, but a few of the pre-schoolers at the Northern Virginia Jewish Community Center's Purim workshop are having trouble remembering his name. Teacher Celia Cantor is telling a story about a long, long time ago when there was a king named Ahasuerus who had a queen named Esther . . .

"She was a Jewish lady and very beautiful, and she had a cousin named Mordecai -- "

"He was a bad guy," interrupts four-year- old Marc Doniger, who knows there must be a villian in the piece and is eager for the fray to start.

"Oh, no, he was a very good guy," corrects Cantor. "The bad guy was named Haman, and he planned to kill all the Jewish people. But Esther begged the king to stop Haman, and she was so beautiful and he loved her so much that he agreed. Then Esther's cousin, Mordecai, found out that Haman was going to kill the king, too, so the king got rid of Haman. Every Purim we think about the people who helped us."

"I killed that bad guy Mordecai," announced Marc, with a triumphant, zapping gesture.

"You should't have -- he was a good guy. Here's a picture of the bad guy," says Cantor, holding up a children's book on Purim. "What's his name?"

"Haman," shouts everyone, and Cantor tells them that every Purim Jewish people have a party and put on costumes.

"On Halloween you put in costumes," adds five-year-old Lea Buzzell.

To introduce another Purim costume, Cantor sings a song with the word "hamentaschen" in it, and explains to the children that hamentaschen are cookies in the shape of a triangle -- the shape of Haman's hat.

"We're going to make some Purim costumes, but first we have to see about our snack. What sort of snack do you think would be just right for Purim?" asks Cantor.

"Chocolate pudding," suggests three-year- old Sara Rothstein.

"Peanut-butter sandwiches," votes three- yea-old Jonathan Lurey.

"I know -- hamentaschen!" says Marc.

When hands are washed, Cantor divvies up the dough.

"This is real dough -- not play dough," she says. "It tastes better when it's cooked, so try not to eat any."

When the kids have had a few minutes to play with the dough, Cantor shows them how to roll it into balls, flatten the balls into circles, roll the dough and cut it into round shapes with plastic cups.

"Each child should make two -- one to eat and one to take home," instructs Cantor.

"I'm going to eat two," announces Marc.

"I need four, because I have a Mom and a Dad and a brother," protests four-year-old Benjamin Miller.

Cantor helps the kids put a dab of either plum or apricot jam in the center of each circle and then squeeze the corners together.

"What shape did we make the circle turn into?" she asks. "That's right, a triangle. Don't they look just like Haman's hat?"

The cookies are safely in the oven, but Marc is anxious: "I hope Haman don't get the cookies. I'll blast him," he threatens, then crawls under the table.

"He's pretending Haman is under there," explains Sara, and Cantor, who wants to get on to the next activity, retrieves Marc.

"Haman isn't really around here," she explains. "He lived a long time ago. No bad guys are coming, and we hope they never will come."

But when the kids start making Purim costumes out of paper bags, bad guys seem to be making a comeback.

"I want to be the man who kills the king," says Jonathan.

"The king doesn't get killed," explains Cantor, "but if you want to be the bad guy take a black triangle and glue it to the top of the bag for your hat."

Mordecai's hat is a green half-circle, and the king and queen both have crowns. The kids make the eyes, nose and mouth wi are out of the oven and Marc has a more pressing question: "Can we eat now?" he asks.

CELEBRATING PURIM

"Let's Make Hamentaschen," a workshop for three- and four-year-olds, will take place Sunday from noon to 1:30 at the Northern Virginia Community Center, 8822 Little River Turnpike, Fairfax. Children will make the cookies, sing songs and listen to Purim stories. To register, call 323-0880.

The Jewish Community Center in Rockville will hold a family Purim party Saturday from 6:45 to 8:30 and a Purim hats and masks workshop for six- to 16-year-olds Sunday from 1:30 to 4:30. For information call 881-0100. To help children learn more about Purim, celebrated this year on March 9, the Board of Jewish Education recommends the following books:

Purim Parade, by J. Bearman; Purim, by S. Cederbaim, A Pitzel Purim, by L. Jaffe; Let's Talk About Jewish Holidays, by D. Kripke; and Happy Purim Night, by N. Simon.

HAMENTASCHEN: Sift four cups flour, 1/2 teaspoon salt and 1 teaspoon baking powder into a bowl. Add 1/2 cup shortening, 4 eggs, 1 cup honey and blend together. Work with hands to form a dough. Roll out and cut into circles with a cup. Place a heaping tablespoon of apricot or plum jam or canned hamentaschen filling on each circle and pinch together to form triangles. Place on greased cookie sheet and bake in a pre-heated 350o oven for 20 minutes.