In the end, it all comes back to the singing.

Placido Domingo has been singing professionally for 54 years. He does other things, of course. He conducts, and he’s an administrator, although, of course, he’s about to step down as general director of Washington National Opera after 15 years with the company. But the bottom line is that he’s 70 this year, and he still sounds pretty darn good.

How? He has no idea.

“I ask myself that question,” he says, “why am I still singing. Well, I am singing because I can. But why I am still able to sing, you know, this is a big mystery for me.”

Washington hasn’t heard Domingo sing for a while, but he will correct that Friday when he performs the role of Orestes in Gluck’s “Iphigenie en Tauride,” which he has never sung in Washington but reprised this season at the Metropolitan Opera in New York. The role, originally written for a baritone and then revised for a tenor, fits Domingo’s current vocal state just about perfectly. “I kind of do a combination,” he says, of the two versions.

There have been a lot of valedictories written about the day Domingo stops singing. For a while, he said he was going to take his leave with the baritone role of Simon Boccanegra. Then, it was going to happen in his 70th year. But he’s done Simon, he’s turned 70 and he’s still going strong, seeking out new parts, ranging ever further afield: taking on baritone parts; essaying Baroque opera.

So it would be premature to see this “Iphigenie” as any kind of leave-taking. Yet it is the last role he’ll sing here as general director: the end, in a way, of an era.

Domingo has stopped making any predictions about his vocal longevity. He certainly isn’t sparing himself. He thinks over the question while sitting at WNO’s rehearsal studios in Takoma Park in a brief hour between two rehearsals, one for “Iphigenie” and one for “Don Pasquale.” Domingo being Domingo, he’s not ending his official Washington tenure with just one opera — he’s conducting “Don Pasquale” as well. Sitting in an upholstered chair in a windowless office, he speaks in his trademark caressing voice, softened by his Spanish accent to a sinuous lilt.

“It could finish,” he says of his singing abilities and means at any time, without warning. “A few years back, I was doing ‘Parsifal’ in Los Angeles, and it was a production of Robert Wilson. And he wants the singers to be very static, you know, which is his style, which I love. But it was my first time with him. And when I do Parsifal, I am always on the floor, I move a lot, especially in the second act with Kundry . . . and I have to be like this.” He mimes the frozen, stylized gestures that Wilson typically requires of singers. “I arrive to the fifth performance, and I have to announce before the third act that I am not feeling well. Okay, so it will pass. Three days later, the sixth performance I was in the theater, and I had to announce myself, ‘Ladies and gentlemen, I am here, in the theater, but I am sorry, I cannot sing.’ And the last performance, the same, I could not sing.”

“I thought I [had] finished my career,” he continues. “I thought, ‘Well, that’s it, Placido; it’s time; I mean, it’s time.’ What can I do? Just be thankful that I did so many years, and that’s it. But little by little, it came back again. So you never know. [Every] day now, I’m thankful, and it’s an extra day. But I do not know when is going to come the day when I wake up and there is not any more the voice.”

There are several factors involved in Domingo’s ability to sing at an age when most singers have retired or appear only in cameo, character roles. One is a deep passion for music and opera — “it is almost an addiction,” he says, smiling, describing the quality of opera that makes so many people care so passionately about this eccentric art form. Another is a drive to communicate, to reach every single person he encounters — in the theater, backstage, in person. Sitting facing an interviewer, his focus is complete: He looks into your eyes, he speaks graciously, even to a critic whose writings have, at times, caused him considerable displeasure. He often starts conversations with a personal touch, commenting on a spouse or child, a detail that it’s hard to believe he could remember.

That drive is manifest to those he works with as well. “Mainly what I got from him,” says the soprano Amanda Squitieri, “is that you can’t communicate anything unless the intention of the words is completely clear. He’s a storyteller.”

Squitieri, an alumna of Washington National Opera’s Domingo-Cafritz program for young artists, is one of the many singers Domingo has mentored. She was accepted into the program after an impromptu audition backstage at the Met before he was going onstage to sing “Parsifal.” Most recently, she appeared with him in “Il Postino,” the world premiere of which was performed last fall in Los Angeles.

“I think what surprised me the most,” she says, “was how human he is, how gracious, and how he treats everyone as if they’re the most important person in the world.”

“For me,” Domingo says, “the public is everything.” He adds: “The anticipation of the public to hear you is amazing. You accept a contract, and the moment you accept the contract, the public are already making a big effort to get tickets. And every three days, every four days, you are singing something, somewhere. Can you imagine how much all those people are part [of what we do]? They have complicity with us.”

But the third factor in Domingo’s astoundingly long vocal career, and perhaps the key one, is his canny, visceral understanding of how his own voice works. It was hard-won knowledge. Opera fans know well that Domingo began his career as a baritone. “Let’s say that my voice, the color was of a tenor, but the tessitura was very difficult for me,” he says. “So I worked half-step by half-step by half-step,” moving his voice up the scale toward those all-important high notes. This explains the dark honey sound of his singing, a timbre burnished by time, sitting in the range of a baritone but with the unmistakable ping of a tenor.

This knowledge is not something he can easily put into words. It’s an understanding based completely on the mechanics of making sound. Asked what adjustments he’s made to his technique over the years, he points to the greatest and most versatile of all tenors, Enrico Caruso. “I tried to imitate what he was doing,” Domingo says, “and I found that I could sing easier. What he was doing, he was stopping the sound a little bit, without giving so much vibration in the voice.”

He proceeds to demonstrate, singing, full voice, the opening line of “Rachel, quand du seigneur” from Halevy’s “La Juive,” one of Caruso’s iconic arias, until the drywall resounds. “That’s me,” he says. He then sings it again, no less loudly, but with a straighter, slightly more covered or pushed sound that indeed evokes the late Caruso. It’s not a question of copying, but of incorporating. The point, he says, is not to sing like Caruso, “but it helps me in some moments to do it” — like an artist mixing different colors on his palette.

As more and more young singers burn out — Domingo still hopes that Rolando Villazon, who briefly seemed a possible successor to his tenor crown, will recover from the vocal difficulties that have kept him largely off the opera stage for some time — one has all the more appreciation for Domingo’s savvy. Some people in the past have criticized an apparent megalomania, a drive to sing the most, do the most, be the most; but with hindsight, his versatility and drive seem to have been strengths. Certainly the repertoire he’s seeking out now — early works such as “Iphigenie” — are better suited to him than would be endless reprisals of the roles of his heyday. “I cannot sing the repertoire that I used to sing before like I used to sing it,” he says matter-of-factly. “So then you don’t do it.”

But he hasn’t stopped looking for new roles. Handel’s Samson, Gluck’s Orfeo and some of Verdi’s other baritone roles are all on the agenda.

“I still think that one of these days I will say, ‘You know what? I have done 200 and something Otellos, so I don’t mind now, I do [one more], and that will be my last performance ever,’ ” he says. “I don’t know. I don’t even know what I am going to do one day to finish. I think that I am not going to be the kind of a singer who will go around the world to say [goodbye]. I think that one day, I will have the feeling that that’s it, and I will go out and I will say to the public, ‘Ladies and gentlemen, that was my last opera performance.’ ”

That day will come, someday. But not today. Now, Placido Domingo is off to rehearse.

Washington National Opera

Placido Domingo stars in “Iphigenie en Tauride,” Friday through May 28, and conducts “Don Pasquale,” May 13 through 27, at the Kennedy Center Opera House, 202-295-2400 or