"HALLOWEEN IS even bigger than Christmas for us," says Jean Rosenthal, owner of Backstage, the theatrical specialty store at 2101 P St. NW. The shop -- which normally sells scripts and makes costumes for local theaters -- offers consultation on Halloween makeup every year, and rents getups from a pool of 450 costumes, many of which have been in plays like Horizons' "Absent-Minded Sweethearts," movies like "St. Elmo's Fire" and a variety of TV commercials and industrial films.

"We just did a great Tina Turner bunny rabbit," Rosenthal said. Some of this year's popular themes are punk monks, Kabuki actors, singing raisins, Max Headroom, barbarian women and military uniforms.

Rosenthal says she expects more than 3,000 people to line up for makeup and costume tips this weekend, so you may not be able to get in. But stop by and see theatrical set designer Matt Cooper's animated shop window, three views of a haunted mansion with a flickering fireplace, eerie portraits, a vampire and a quivering protoplasmic ghost.

Arena Stage producing associate Jim Nicola is leaving February 1 to become artistic director for the New York Theatre Workshop, a professional off-Broadway theater company devoted to producing new plays and developing emerging playwrights and directors.

"The last seven years at Arena Stage and here in the Washington theatrical community could not have been better preparation for assuming the leadership of a theater," Nicola says. It's a great thing for Nicola, and we wish him well, but it's a major loss to Washington. Nicola directed successful productions of " 'Night, Mother," "Stray Dogs," "The Marriage of Bette and Boo" and the upcoming "American Splendor" for Arena; he has also been a vital force in our theater community, directing shows for Round House Studio and New Playwrights' Theatre, and continually encouraging Washington actors.

"I never started out to write," says actor/playwright Harvey Fierstein, author of the Tony-winning "Torch Song Trilogy," and the musical "La Cage aux Folles," which is at the Warner Theatre through Sunday. The reluctant playwright recently finished rewriting his second multimillion-dollar musical, Peter Allen's "Legs Diamond," tentatively scheduled to open on Broadway in the spring. His most recent play, "Safe Sex" goes into production in London soon (Source Theatre's planning a January production).

"I failed English and creative writing," Fierstein says. "And I never dreamed of being an actor. I had always planned to be nonverbal artist. When I was 13 I started in community theater -- only because I wanted to make posters and paint the sets. My friend was too chicken to try out for the role, so I tried out." That role was the newsboy in "Our Town." "Five lines. The first role of millions of actors," he laughs.

"The thing I like about 'La Cage,' " says Fierstein, who was a leader of the Lesbian and Gay March on Washington, "is that with all the other s - - - going on in my life -- yelling at President Reagan, the sick friends, the deaths I have to deal with every day -- I walk into that theater, I sit myself down, and it makes me smile and giggle and applaud like nobody's business. The longer the show runs, the criticisms -- that it wasn't brave enough, that it was about an old-fashioned view of homosexuality -- become sillier and sillier. Whenever I'm in town I stick my head in the back of the theater, and after five years of watching it I still cry at the end."

Looks like another long, dark winter for the National Theatre. The box office says there's nothing on the schedule. President and exutive director Donn B. Murphy says the Shubert Organization, which manages the theater and supplies the majority of its shows, is working on it. "It costs them as much as it costs us when we stay dark, but they don't want to bring in an undistinguished production. And I was just in New York and things looked a little bleak up there." The long-awaited musical "Chess" is being rewritten again, and may yet arrive in February; so far the only winter booking is a two-night visit by Catholic University's National Players, doing "Othello" (December 10) and "Dracula" (December 11).

When director Bart Whiteman's new HBW3 Group (it stands for "Harold Bart Whiteman III) came to perform at Javarama on Thursday, they found the avant-garde cafe's doors locked, so the show had to be canceled, and the audience escorted into a show at the Source Theatre.

Whiteman says he had a verbal agreement with Javarama director B. Stanley to perform "Bikini Girls From Mars and Other Unearthly Delights" for five weeks.

Stanley says Whiteman had originally planned to do "The Rat in the Skull," but then switched it for "Bikini Girls," a program of four short plays from the Source Theater Festival. The replacement didn't sit well with Stanley, and he closed the doors on the troupe. Whiteman says he is looking for another location.

Stanley says the Javarama building, at the corner of 14th and T St. NW, has been sold, and the new owner plans to develop the top floors as apartments. Stanley's lease extends through next October, then the performance studio will move to a new space -- he's looking at a large building near 7th and P NW, and plans to continue the Javarama's eclectic programming in an informal performance space and a large formal theater. Next up at Javarama is Marc Speigel's "Rocks," a one-act play "about Sex, God and Rocks," which opens November 20. Call 797-7262.

Bulletin Board: Washington Stage Guild's Halloween Masquerade Ball features a Theatrical Tunnel of Horror -- it's lined with bad reviews. The party, which benefits the theater's current season, is Saturday at 9 at Carroll Hall, 927 G St. NW. Call 529-2084 . . . Artistic director Joy Zinoman, after the last of four elaborately catered galas for her new Studio Theatre: "For four nights we've been opening. Can we be open now? Can we please be open now?" . . . Betty, D.C.'s own "rockapella" stars (and sometime playwrights) are appearing in a self-produced show at Lisner Auditorium November 6 and 7. Tickets are available at Ticketron . . .