Tonight, the Metropolitan Opera will be led by a conductor who has been absent from its pit for 45 years: New York Philharmonic music director Lorin Maazel. The choice may seem a surprising one. On these shores, Mr. Maazel, 77, is primarily regarded as a symphonic conductor. Before taking up the reigns in New York, he led the Cleveland Orchestra and the Pittsburgh Symphony. His appearances at the Metropolitan Opera have been confined to a single season long ago in 1962-63.

Yet in the intervening years, opera has occupied a fundamental place in Mr. Maazel’s career, primarily in Europe. One of his current music directorships — in addition to the New York Phil and the Rome-based young professionals orchestra Symphonica Toscanini — is with an opera house: the Palau de les Arts Reina Sofia, the dazzling new Santiago Calatrava-designed venue in Valencia, Spain, which opened in 2006.

“Valencia has not exactly been a happy hunting ground for opera, but the region is very much behind the effort,” he said. “I formed the orchestra myself over three years. We are attracting a remarkable audience.”

To be sure, he’ll have a remarkable audience tonight when he conducts “Die Walküre” at the Met. It is a work of special significance for him because it is one of the operas that make up the “Ring” cycle: In 1968, Mr. Maazel became the first non-German to lead the “Ring” at the Bayreuth Festival, an invitation he describes as “an enormous honor.” The cycles took place during his first stint running an opera house, the Deutsche Oper Berlin, which he headed between 1965 and 1971, a period that marked his most intense activity with Wagner.

“With too much Wagner, you can get overwhelmed,” he said. “The music drugs you, and you become an addict. You start to believe that nothing else exists. Then it’s time for Verdi and Puccini.”

One opera house that has benefited from his use of the Italians as an antidote to Wagner has been La Scala, where he has conducted three opening nights and 10 new productions since his association with the house began back in the 1950s. He also headed the Vienna State Opera between 1982 and 1984, making him the first American to hold the post.

Mr. Maazel traces his love of opera to early childhood and his father, who taught singing. A child prodigy who was born in Paris and raised in America, Mr. Maazel first conducted the New York Philharmonic when he was 12. In September 2002, he returned to that orchestra as its music director. More recently, he has channeled his musical talents into composition. His opera “1984,” based on the George Orwell novel, had its world premiere in London at the Royal Opera House in 2005.

“I was commissioned to write it. I never would have decided to write it on my own. I got caught up again in the horrific substance of the story — the creeping of the state into the private world of its citizens,” he said. “With a love story in the romantic tradition, it is the stuff of opera. The lovers are doomed to disaster, and they know it.”

His “1984” will be presented at La Scala in May — under his baton. And he views this as a contribution toward keeping the art form vital. “It is important that the tradition be renewed,” Mr. Maazel said of new operas generally. “Historically, very few operas survived. People wanted new operas, and there was not much of a repertory to fall back on.”

Mr. Maazel has been known to be frank about his distaste for extreme forms of musical modernism. A few years ago, he selected Rodion Shchedrin, a stylistically conservative Russian composer with a successful Soviet career behind him, to write a concert opera for the Philharmonic, a choice that baffled some observers.

“I always thought Shchedrin was an excellent composer,” Mr. Maazel said, “but the result exceeded my expectations. What matters is not the musical style but the musical subject matter. Benjamin Britten and Sibelius were out of sync with their times, but most of the music we heard in their place has faded away.”

When asked about stage directors he has admired during his long career, the first name Mr. Maazel mentions is Wieland Wagner. In 1964, they worked on “Tristan” at La Scala with a cast that Mr. Maazel rattles off with justifiable pride: Birgit Nilsson, Wolfgang Windgassen, Rita Gorr, Gustav Neidlinger, and Franz Crass. “Wieland knew very well that the staging comes from the music, and that the music should not be subservient to some modern staging concept.”

Mr. Maazel also mentions the German director and designer Herbert Wernicke, with special fondness for the Salzburg “Don Carlo,” as well as the iconic Italian director Giorgio Strehler: “La Scala still uses the ‘Falstaff’ I conducted.” On his list is another Italian, Filippo Sanjust, who produced “an excellent Covent Garden ‘Luisa Miller.'” Among the current generation, he singled out the visionary Canadian Robert Lepage, who staged “1984” and will produce a new “Ring” for the Met.

Mr. Maazel had a falling out with Franco Zeffirelli when the director made cuts in his 1986 film of “Otello,” which the maestro conducted. “The cuts were in breach of my contract, and I considered suing, but the movie was winding down and I thought the publicity of a lawsuit would start new discussions,” he said. Mr. Maazel has two classic filmed operas under his belt: the Joseph Losey “Don Giovanni” (1979) and the Francesco Rosi “Carmen” (1984).

As for the state of vocal performances these days, he is sanguine. “Europe probably had a finer roster 70 or 80 years ago when there was an accepted method of schooling. Singers started in the opera studio, studied their first parts with experienced coaches, and sang them with experienced conductors,” he said. “Now a singer with a good voice and some talent can become a media star overnight. Still, there are some fantastic people out there today.”

He’ll have some fine voices to work with tonight. The cast includes the Australian dramatic soprano Lisa Gasteen as Brünnhilde, the fine Canadian soprano Adrianne Pieczonka as Sieglinde, and the powerhouse mezzo Stephanie Blythe as Fricka. Bass baritone James Morris sings Wotan, with the able Clifton Forbis as Siegmund. The promising Russian bass Mikhail Petrenko will be Hunding.

The performance is dedicated to Régine Crespin, who died in July. The soprano made her Met debut as the Marschallin in “Der Rosenkavalier” under Mr. Maazel’s baton in 1962, and sang with the company until 1987.

Might the Met performances trigger Wagner relapse in this maestro? “Oh, no,” he said. “There are only five performances. I’ll be able to hold up!”