Emil de Cou made his first appearance with the National Symphony Orchestra five years ago this summer, when he was engaged as a guest conductor at Wolf Trap, leading snippets from Alfred Hitchcock soundtracks as film clips flickered above his head. "I was very excited about it," he reflected this week. "I was building up my career then, conducting wherever I could, and I thought that this would be a great addition. At that point, I expected to conduct the National Symphony exactly once and then move on -- but of course I hoped there might be another appearance someday."

De Cou needn't have worried. In March 2002, he was named the NSO's assistant conductor, and he was promoted to associate conductor in the fall of 2003. He has led the orchestra on residency tours in four states, in subscription concerts at the Kennedy Center and on the lawn of the Capitol. This summer, a new position was created for de Cou -- he is now the NSO@WolfTrap Festival conductor -- and he will be very busy indeed during the next few weeks.

Tonight at Wolf Trap, he will lead the NSO, the Washington Chorus and members of the Wolf Trap Opera Company in a program titled "Murder and Other Operatic Mayhem" -- a neat blend of dramatic scenes from Verdi ("Rigoletto," "Il Trovatore" and others), the great Sextet from Donizetti's "Lucia di Lammermoor" (which has two of the juiciest tunes in the repertory), Wagner, Humperdinck, Puccini, some newly updated Gilbert and Sullivan, and an aria from that grisliest of American musical theater pieces, Stephen Sondheim's "Sweeney Todd." "Think of it as opera meets Jerry Springer," de Cou said.

The following week, he will lead the NSO in three different locales, beginning next Saturday with music by Aaron Copland, Ferde Grofe, Leroy Anderson and others up at Carter Barron Amphitheatre in Northwest Washington. On July 21, he will share the "great indoors" of Washington National Cathedral with the Washington Bach Consort, and the following night he will lead the NSO's annual Young Soloists' Competition in a free concert at the Kennedy Center.

Then it's back to Wolf Trap to close out July with two of the more enticing multimedia events of the summer. On July 29, de Cou will lead what is being called the world premiere of a new version of "The Wizard of Oz," with the NSO playing the orchestral score while the classic 1939 film is projected. The following night will be given over to famous dance scenes from a number of movies, including "Singin' in the Rain," "An American in Paris," even "2001: A Space Odyssey" (in which the spaceships might be said to "dance" in the middle of the cosmos) with the NSO playing live accompaniment.

"I grew up in California, so the movies are in my blood," de Cou said. "And I like conducting outdoors because so many of my most important musical experiences were at the Hollywood Bowl. When I was a kid, I'd just sort of move there for the summer -- it's where I heard so many masterpieces for the first time."

De Cou, 47, was born in Los Angeles, where he took his early training in horn and piano. His first conducting teacher was Herbert Blomstedt, former music director of the San Francisco Symphony, with whom he began to work while he was in his late teens. He attended the Music Academy of Vienna and has served as principal horn of the Baden State Theater and the Mozart Orchestra of Salzburg on a European tour. In addition to the NSO, he has led the principal orchestras of Philadelphia, Houston, St. Louis, Detroit, Montreal and Minnesota, as well as the Boston Pops.

In addition to his duties at Wolf Trap, de Cou remains the NSO's associate conductor. "You do a bit of everything in that position," he said. "A good amount of my time is spent speaking and writing because I believe that an orchestra should have a spokesperson as well as a conductor. It's not enough to make wonderful music -- we have to explain what we're doing as well. Summer concerts bring a new audience, and it gives us a chance to win people over: We want to be welcoming and informal without compromising quality. I consider my leadership a tremendous responsibility and I want to meet people, I want to go on the radio, I want to be on television -- I want to fight for the art."

He laughed. "Of course, I want to study and learn new music as well!"

An associate conductor's duties also include scanning possible repertory for NSO Music Director Leonard Slatkin, and so de Cou goes through the many scores that arrive every week at the Kennedy Center, solicited and unsolicited, sent by hopeful composers. "It's really an amazing collection of material," de Cou once said. "We get everything from handwritten scrawls -- 'Hi. I have a melody that I'd like to sing with your orchestra' -- through new pieces from established publishers like Schirmer and Boosey & Hawkes. I look at the scores and sometimes take them to the piano or listen to them on a CD, if it is available. And then I pass on about one out of every 100 or 150 scores I receive to Leonard to see what he might think."

In keeping with his determination to communicate with audiences, de Cou has written program notes for most of the concerts the NSO has played this summer. Here is a sampling of his introduction to "The Wizard of Oz": "From its 1939 sneak preview in Los Angeles to the world premiere version we hear tonight, 'The Wizard of Oz' remains a marvel -- images, phrases and references to the movie have found their way into the everyday lingo of American life. After two more decades of theatrical releases, yearly television broadcasts began. Long before VCRs and DVD players allowed for instant gratification, these annual broadcasts became national occasions, much-anticipated stay-up-late-in-your-jammies events for the Baby Boomer generation.

"The score is so familiar that it is easy to take for granted," de Cou continued. "Coming as it did only a decade after the dawn of sound, 'Oz' relishes in the new technology and is filled from start to finish with music (78 out of 102 minutes is scored), from songs of every genre to a mini Gilbert and Sullivan operetta -- the Munchkinland section is six minutes of nonstop singing interrupted only by the surprise fiery entrance of the Wicked Witch."

The original orchestral score of "The Wizard of Oz" has been lost -- "The studio threw out its library a few years ago, just like that," de Cou said in disbelief -- so it has been carefully reconstructed by ear for the upcoming premiere. Advanced digital technology permits all the original recorded passages for orchestra to be removed from a film while allowing the singing and speaking to be heard without impediment. That will allow de Cou and the NSO to come in.

"It's very exciting to accompany Judy Garland all these years later," de Cou said. "And the film holds together incredibly well. The ending only gets more poignant -- probably because we've all changed, and the world has changed, but the film hasn't. It's immortal, a great work of art. And hearing the orchestral music played anew by a full live orchestra -- it will be as though yet another whole new layer of Technicolor had been added to our experience!"

NSO conductor Emil de Cou reviews a score with Lt. Col. John Clanton of the U.S. Army Chorus.De Cou, the NSO's associate conductor, says, "You do a bit of everything in that position."