THERE'S MORE than meets the eyes and ears in a performance of "Cats" at the National Theater. For one thing, the orchestra's not in the pit down front, it's up on the fourth floor.

And the voices you hear aren't necessarily coming from the performers onstage; "Cats" employs four singers who supplement the sound from a cloister in a corner behind the percussionist.

"It's such a physical show, and many of the dancers can't wear the bodypack microphone set, so there are times when the sound could disappear entirely if everyone is breathing hard," says "Cats" chorus member Kirstie Carnahan. The booth singers are at work every time there are more than three voices in a song.

"We're separated from the orchestra by a plexiglas wall, so we can watch the conductor {Kristin Blodgette}, and a closed-circuit monitor that gives us a wide-angle view of the action onstage." Carnahan says there are also three monitors in the wings so the onstage players can see what the conductor's doing.

There's a decidedly casual atmosphere in the singers' booth, which is decorated like a giant aquarium, with plastic fish suspended from threads, sandpaper "gravel" on the floor, windup toy crabs, and seashells provided by an orchestra member.

"On the first night, we wore Speedo swim goggles during the show," Carnahan says. When a line comes up, the singers step casually to the mike, then go back to their books or magazines or visits with the "Cats" crew. Carnahan said she devoured "War and Peace" in four weeks in Philadelphia, and is now reading up on the Iran-Contra chronology.

All the booth singers are understudies. Carnahan -- who was nominated for a Helen Hayes Award this year for her performance as Audrey in Olney Theater's "Little Shop of Horrors" -- understudies Grizabella and went on for several weeks in Detroit and Philadelphia, and has stepped in three times here so far. Raissa Katona understudies Jellylorum and Jennyanydots, and is married to Frank Mastrone, who plays Gus the Theater Cat. Skip Harris understudies Bustopher Jones, Gus and Growltiger; and R.F. Daley understudies Old Deuteronomy.

Carnahan says she'll remain with the "Cats" company till October 3, when she begins work with the national touring company of "Les Mise'rables." She'll be a member of the ensemble, and will understudy Fantine, who will be played by Diane Fratantoni (who, coincidentally, played Grizabella the last time "Cats" came to town).

Burlesque is back: The vanishing American entertainment genre that produced Red Skelton, Jackie Gleason, Red Buttons, Phil Silvers, Fanny Brice and Sally Rand has found new life on the national dinner theater circuit, and Washington gets a taste as "Best of Burlesque" moves into Petrucci's Dinner Theater in Laurel through September 27.

"We're not claiming that we're the best," says David Hanson, an ex-Red Sox ballplayer, who, in addition to being producer and director, plays straight man and second banana in the show. "We're putting together what we think are the best of the dance routines, the best of the comedy acts from the great days. Certain sayings that were current in burlesque's heyday in the '30s and '40s wouldn't be understood by today's audiences, so we've updated it a bit."

But "updated" doesn't mean "dirty," Hanson says. "It's about comedy and pretty girls -- but without profanity. Our show is 80 percent comic, with a dancer, a top banana and second banana, a straight man, a chorus line of five girls, and specialty acts. We do take sexual situations, but we portray them in double-entendre," says Hanson, who says he refuses to go along with the current vogue for vulgar and explicit material.

Hanson gets steamed about the bad rap given the venerable striptease. "I think people have lost the meaning of the word -- it's strip-tease. People think it means get naked. It's an insult to an American art form."

Dancer Sandy O'Hara, who performs the fan dance and other variations on that American art form, defines burlesque "like Webster's says: to make fun of, to mock, with songs, skits and dances." O'Hara, who started in the burlesque biz 21 years ago as a chorus line dancer in a traveling show, once worked for Minsky's revues at Aladdin's Hotel in Las Vegas, and worked with Ann Corio, who recently retired her famous "This Was Burlesque" touring revue, the last representative of the old-style shows. "We loved the idea of bringing burlesque back," says O'Hara. "I just refuse to work any of these 'joints.' "

The show also features Clarence Loos, who was a standup comic "until it got so that there was no place to stand up anymore." Loos says that once upon a time, comedy was about good jokes, now it's about a quirky persona.

"We don't have any message with our show," Hanson says proudly. "People don't have to look at our show and think."

Bulletin Board: The folks at Studio Theater, which is moving across the street to its newly constructed theater, have been finding all sorts of fascinating stuff around the old place, so the theater will hold a dramatic garage sale Saturday from 10 to 6 at 1401 Church St. NW. Several hundred items will be sold, including the patio furniture from "Lemon Sky," the marble slabs from the "Slab Boys" trilogy, the black body-bag from "Landscape of the Body," plus costumes, movie posters, office equipment and other theater paraphernalia . . . Arena Stage company member Robert Westenberg has been cast in the new Stephen Sondheim musical "In the Woods," which begins previews at Broadway's Martin Beck Theater September 29. Westenberg plays a prince and a wolf, and will be reunited with Bernadette Peters, his co-star in Sondheim's "Sunday in the Park with George" . . . Adams-Morgan's trans-cultural Sanctuary Theater is the latest addition to the League of Washington Theaters, and has announced a six-play season to start September 24 with "An Evening of Chekhov and Gorky." Call 745-3666 . . . And Source Theater's new executive director Pat Sheehy has announced seven plays for Source's 11th season: the Washington premiere of Amlin Gray's "How I Got That Story," directed by Stephen Hayes (begins September 9); Clifford Odets' "Golden Boy" (October); Tina Howe's "The Art of Dining" (November); the local premiere of Harvey Fierstein's "Safe Sex" (December); Jean Anouilh's "Time Remembered" (January); Marsha Norman's "Getting Out" and a trio of plays by August Strindberg (April). It's an impressive list, and Source is offering its first-ever subscription series. Call 462-1073.