DIVERSIONS : Curtain Calls : Ever wanted to peek backstage? Now you can on free tours of performing arts complexes.

According to an old show biz saying, what goes on behind the scenes is often more interesting than what’s happening onstage.

You can judge for yourself.

Several performing arts complexes in the Los Angeles area host free tours offering entree to the other side of the footlights. If you’ve ever wanted to view the “Phantom of the Opera� chandelier up close and personal or see what a star’s dressing room is really like, savor these tours.

* The tour of the downtown Music Center of Los Angeles County begins at the elegant Dorothy Chandler Pavilion, home base of the Los Angeles Philharmonic, L.A. Music Center Opera and L.A. Master Chorale.

The 3,200-seat auditorium is the setting for a short course in theater shapes, seating, lighting, acoustic and curtain design. There are two of the latter: a bronze and gold, sunburst-designed main stage curtain that weighs 3,000 pounds, and a anti-fire version, which descends if the onstage temperature rises too high.

The stage is one of the largest in the country; its distance from front to back is equal to the distance from the front of the stage to the back of the house.

Sights on the second level include the Grand Hall crystal chandeliers and the plush, antique-filled Founders Room, where visiting dignitaries are entertained. The entire building is a haven for art as well as music lovers, with sculptures of music figures, 17th-Century tapestries, collages of antique instruments and a display of more than 500 sculptured, gold leaf-covered “Sunbirds� above the refreshment stand.

Across the Music Center plaza, the 747-seat Mark Taper Forum, home to the Center Theatre Group, has a thrust stage that juts out to the audience, illuminated by 300 overhead lights; in the lobby are the Tony Awards won by the company and its productions.

At the 2,100-seat Ahmanson, whose own Center Theatre Group has been displaced by “The Phantom of the Opera,� visitors can stand under that show’s pivotal chandelier prop of more than 30,000 plastic beads and learn some of the production’s special effects secrets.

Music Center of Los Angeles County, 135 N. Grand Ave., Los Angeles. Tours are held Mon.-Sat., but days and hours vary. Access to each theater depends production schedule. (213) 972-7483. * The Music Center’s counterpart to the south is the Orange County Performing Arts Center, striking proof of what $72.8 million can do for a former lima bean field.

The facility’s main attraction is the multipurpose Segerstrom Hall, where the Pacific Symphony, Pacific Chorale, Orange County Philharmonic, other local groups and touring companies appear.

An impressive sight is the five-story Grand Staircase, lined with beveled mirrors that create a prism effect.

Upstairs, you can learn such tidbits as the origin of the word proscenium during a lecture on the building’s architecture. Overhead, a fascinating kite-like formation called “The Firebird� changes appearance depending on the sky it reflects. In the 3,000-seat auditorium, discover why the hue known as “theater red� is a popular upholstery choice.

Touring an upper level provides a heady view of seating sections jutting at different angles for acoustic purposes, as well an encounter with the sound-mix booth and its tunnel leading from the audience to backstage. Down by the stage, learn particulars about orchestra pits, theater formations, scene changes and lighting.

A backstage visit includes a peek at dressing rooms for stars, principals and chorus; a lounge; wardrobe room, and rehearsal halls. The walls are painted according to a theater tradition: One is light and the other dark, so that performers unfamiliar with the building know that to head toward the stage, they need only keep the lighter wall to their right.

Also backstage is the complex’s other theater--Founders Hall, which doubles as a rehearsal room when it is not hosting children’s theater or serving as a television studio.

Orange County Performing Arts Center, 600 Town Center Drive, Costa Mesa. Tours: Mon. and Wed. at 10 a.m. and 11 a.m. and the first Saturday of the month at the same times, but schedule is subject to change. Reservations required for 10 or more. Information: (714) 556-2122, Ext. 833. * On a less grand but more historic scale is the Pasadena Playhouse, proclaimed by the state Legislature as the State Theater of California. Built in the Spanish Colonial revival style, the theater became the first in the United States to stage all of Shakespeare’s 37 plays and was recently a location for the film “Noises Off.� Its tour is conducted by alumni of the defunct School of the Theatre, who impart firsthand anecdotes of earlier Playhouse performing days.

With their original, colorful Spanish-motif paintings, the ceiling beams in the green room are real standouts. Visitors can step inside one of the adjoining dressing rooms.

Learn about backdrops at the scene dock, where the theater’s first light board is on view. Upstairs, a bare-bones rehearsal room was formerly the costume department, with the biggest wardrobe selection in Southern California.

After visiting the green room and auditorium of the 120-seat Balcony Theater, the tour concludes in the 450-seat main stage house, where you may catch crew members working onstage with lights and other paraphernalia.

Pasadena Playhouse, 39 South El Molino Ave., Pasadena. Tours are scheduled sporadically, by appointment only for individuals and groups. (818) 763-4597.

* And while in Pasadena. . . . the Ambassador Foundation runs a tour of its grounds, including an in-depth visit to the Ambassador Auditorium, which hosts performances by the Los Angeles Chamber Orchestra and numerous other artists.

Ambassador Auditorium, 300 W. Green St., Pasadena. Tours are by reservation only, Mon.-Fri., 10 a.m., noon and 2 p.m., and Sun., noon and 2 p.m. (818) 304-6123.

* The 30-year-old Bob Baker Marionette Theater, the country’s oldest ongoing theater of its kind, does not have an actual tour. The downtown Los Angeles theater does, however, offer kids--and interested adults--a post-performance demonstration of marionette and other puppet techniques.

You can also ask questions and watch puppet personnel craft and clothe marionettes; once upon a time, costume designer Ursula Heinle did the handwork on Nancy Reagan’s first inaugural gown.

Bob Baker Marionette Theater, 1345 W. First St., Los Angeles. Performances Tues.-Fri., 10:30 a.m., Sat.-Sun., 2:30 p . m. Groups can also book other times. Admission: $10 for children and adults, $8 for seniors; includes refreshments. (213) 250-9995.