On the Day of Purim in 1946, less than a year after the fall of the Third Reich, something like half of the Jews still alive in Europe threw a vast and noisy costume party in the displaced-persons camp at Landsberg, Germany.

"It was like Macy's Thanksgiving Day parade," one of the celebrants recalled, "except nobody was watching. We were all in it."

There was another difference: For costumes, most of the folks put on the shapeless striped uniforms they had worn in the death camps; others dressed up in the garb of the Nazis they had so recently escaped.

"Hey, that's Purim for you," said Anna Cohn, director of the Klutznick Museum in B'nai B'rith International's Washington Headquarters. "Purim is resilience, it's the joy of freedom. It's the one day of the year when a Jew will do things that would be a little scandalous at any other time. On Purim the Law says, 'Be merry, make joyous celebration, drink too much, turn things topsy-turvy.' " "And while it isn't actually in the Law," added associate director Linda Altshuler, "it's also the day when we could get away with poking fun at the rabbi."

On Sunday the Klutznick will open a rich exhibit on the Purim festival that traces the celebration from the time of Esther, who started it all. Designer Chris White has worked magic in the limited spaces, creating a Persian courtyard that looks delicate but is meant for children to clamber over.

The exuberance of Purim extends to the scrolls that recount the story of Esther, because the stricture against fanciful illustrations does not apply since God's name is not mentioned. The jewel of the exhibit is a lavish deerskin scroll from 18th-century Italy, more than 20 feet long and including scenes believed to be unique.

The exhibit also has films and a stage on which children are invited to don costumes and act out their own plays.

FESTIVAL OF PURIM

Klutznick Museum, 1840 Rhode Island Avenue NW. Open 10 to 5, Sunday through Friday except holidays.