NINETY PERCENT of the plays produced professionally in the U.S. are presented with all-white casts -- many of those productions are in cities like Washington, with at least 50 percent nonwhite populations. Somehow, in 1987, that state of affairs doesn't seem quite right.

The League of Washington Theaters is addressing the controversies and challenges of this crucial issue with a day-long symposium on "nontraditional casting," November 22 at Arena Stage's Kreeger Theater.

The symposium will imaginatively illustrate various methods of nontraditional casting, such as "cross-cultural casting," transferring the "world" of a play to another culture, as in Ford's Theatre's "Hot Mikado," and the Olney Theater's "The Boys From Syracuse," both of which were transplanted to 1930s Chicago; "conceptual casting," casting an ethnic actor in a role to give the play greater resonance, as when deaf actor Howie Seago starred in "Ajax"; or "colorblind casting," which has long been practiced by the Arena Stage, the Shakespeare Theater at the Folger and others.

A multiracial mix of Washington's best actors will perform scenes from familiar plays like "American Buffalo," " 'night, Mother," "The Misanthrope," "As You Like It" and "Our Town," staged by noted directors Samuel P. Barton, Glenda Dickerson, Michael Kahn, Vera Katz, Mike Malone, Hugo Medrano, Harry Poe and Douglas C. Wager. The symposium's free, but advance registration is required. 527-0440.

While we're in a nontraditional mode, let's note that actor Vince Brown will conduct a free program on black Shakespearean actors Thursday (November 19) from 12:15 to 1 as part of the Midday Muse series. 544-4600.

"All I wanted to do was sell a few books and avoid embarrassment," says Harvey Pekar about his first appearance on the David Letterman show. Pekar -- a Cleveland file clerk who writes and publishes "American Splendor" comic books, and is the subject of the play "American Splendor" at Arena's Old Vat Room -- will be on Letterman Tuesday, his fifth go-round on the show.

"I live in Cleveland and I've seen it all," Pekar writes in the August 25 Village Voice. "So I wasn't surprised when Letterman started asking me these dumb questions like "How are things in Cleveland?" They were so silly I started giving him incredulous looks and ridiculing him, saying he was a show biz phony and complaining about the lousy money he paid ($100 for the first appearance). The audience ate it up. Here was this sour-faced, sloppily dressed file clerk turning the tables on Mr. Condescending Wise Guy. Letterman, who's, off-camera, a quiet, thoughtful man, held me over five minutes and publicly asked me to return."

Letterman has sinced upped the ante to $490 for Pekar's appearances, but because of the hectic activity surrounding the Arena opening, Pekar declined an invitation to go on the show last week. But Pekar had heard that Arena development specialist Josh Milton had a "stupid people trick" -- Milton plays musical numbers on his jawbone. "I have perfect pitch and a hollow head," Milton says. Pekar called Letterman's offices and had Milton audition over the phone while the Arena office cheered; Milton has been asked to send a videotape audition to New York for the show.

On Monday, "Shear Madness" breaks the box office record held by "Life With Father" -- that makes the show the longest-running play in the United States, with 3,225 performances. To celebrate, writers/producers/stars Bruce Jordan and Marilyn Abrams are flying all three of their "Shear Madness" casts, including the Kennedy Center troupe, to Boston for a performance and party.

Bulletin Board: Following the new, improved musical adaptation of "A Christmas Carol" (returning after a two-year absence) and a brief January engagement by Mark Russell, Ford's Theatre will present "Elmer Gantry," a new musical adapted by director David Bell. The February opening will coincide with the 20th anniversary of the reopening of the theater . . . Dramarama: the first University of Maryland Drama Conference is coming up November 21-22 at Tawes Theater. The agenda includes panel discussions on East-West drama, music theater, postwar drama, audience response and theater and politics. Notable panelists include Eric Bentley (who's just reissued his 1946 "The Playwright As Thinker: A Study of Drama in Modern Times," including his controversial foreword which tolls the death knell for the postwar Broadway theater); Shakespeare scholar Sam Schoenbaum; Peter Frisch, artistic director at New Playwrights' Theater; and Misako Watanabe, a leading Japanese stage actress, who will perform the one-character play "Make Up," November 22. It's open to the public; call 454-1820 to register . . . And The Young Lawyers Section of the Bar Association of the District of Columbia presents its annual musical revue "Probable Flaws," which they tell us is about "the bicentennial of the Constitution and the lives of Washington lawyers." Sound like fun? The show, which benefits the Dance Exchange, is Thursday through November 21, at the Duke Ellington School of the Arts. 223-1480.