In 1969, the musical theater composer-lyricist Jerry Herman achieved a Broadway milestone. With the opening of “Dear World” — joining his earlier “Hello, Dolly!” and “Mame” — he had three shows running at the same time.But the celebration didn’t last long: “Dear World” was a flop.Over-revised because of conflicting artistic visions and commercial pressures, it didn’t have the easier success of Herman’s hits, despite its elegant, French-inflected score and Angela Lansbury’s Tony Award-winning lead performance. Other beloved shows would come later — particularly the pathbreaking “La Cage aux Folles,” which in 1983 brought a gay love duet to Broadway — but as the decades went on, “Dear World” became a curiosity rather than canon.That, of course, is what New York City Center’s Encores! specializes in: brief revivals of Broadway rarities, grandly orchestrated and luxuriously cast. And that is where “Dear World” will return to the stage on Wednesday, as the first production to be conducted by the series’ music director, Mary-Mitchell Campbell.Campbell rehearsing the orchestra for “Dear World.” Her break conducting musicals came when she worked on a benefit concert of “Sweet Charity” with its composer, Cy Coleman.Amir Hamja for The New York Times“The thing to me that is most exciting about all this,” Campbell, 48, said, “is the celebration of the music and the celebration of live musicians making that music, in the way that you do at the symphony.”Campbell was brought up in the classical world, as a piano student bound for the concert hall stage; but she was also attracted to different types of music — especially musical theater. Which is what she was aiming for when she moved to New York after school. Just a few weeks later, a break came when she was brought on for a benefit performance of “Sweet Charity.” She found herself in a room with two legends: Cy Coleman and Gwen Verdon.More on N.Y.C. Theater, Music and Dance This Spring‘The Invisible Project’: The new show by the choreographer Keely Garfield at NYU Skirball is a dance, but it is also informed by her work as an end-of-life and trauma chaplain.Life in Photos: Larry Sultan’s photography, now starring in the play “Pictures From Home” and a gallery show, raise issues of who controls a family’s image.Musical Revivals: Why do the worst characters in musicals get the best tunes? In upcoming revivals, world leaders both real and mythical get an image makeover they may not deserve, our critic writes.Rising Stars: These actors turned playwrights all excavate memories and meaning from their lives in creating these four shows, which arrive in New York in the coming months.Coleman became a mentor of hers, and he wouldn’t be the last Broadway luminary to do so. Others have included Stephen Sondheim, whom Campbell worked with on “Company” in its Tony-winning 2006 revival. For that show, she and the director, John Doyle, took an idiosyncratic, chamber approach to the score in which the singers doubled as instrumentalists — even its lead, Raúl Esparza, who sang “Being Alive” from a piano.Now, she has arrived at Encores!, where her top priority is to lead a production of “City of Angels,” among other plans including a new outing for Kurt Weill and Alan Jay Lerner’s “Love Life,” which had been scheduled to open in mid-March 2020 until the pandemic shuttered live performances.But first “Dear World,” about an effort to thwart oil-drilling in the Parisian neighborhood of Chaillot, which reunites Campbell and Donna Murphy, who is starring as Countess Aurelia, the role originally played by Lansbury. They had collaborated on Sondheim’s virtual 90th birthday celebration in 2020, “Take Me to the World,” in which Murphy sang “Send in the Clowns,” a performance the two had rehearsed, trickily, over phone and video calls.“We had been circling each other for a long time,” Murphy recalled. “But we got on very well, and I could see that she was an immense talent, who has such grace and humor.”When Murphy heard that Campbell would be the next music director at Encores!, she thought, “What a brilliant choice.” In between filming sessions for the next season of “The Gilded Age,” she has been hard at work on her Countess Aurelia, a role she has long admired. “I’ve been exploring this part, and the time in which the play was written,” she said, referring to Jean Giraudoux’s “The Madwoman of Chaillot,” the musical’s inspiration. “I love research.”Amir Hamja for The New York TimesAmir Hamja for The New York TimesThis Encores! production has required even more research to effectively create a new performance edition of the book and score. In an interview, Campbell discussed that and more about “Dear World.” These are edited excerpts from the conversation.Did you plan for “Dear World” to be your first Encores! show?It was intentional to do a score that I was excited about. Encores! has done so many amazing scores over the years, that it’s hard to find something, and this was one that was on my list that had never been produced. I have always loved the score.We spent time restoring “Dear World.” There was a lot of detective work, because there were a lot of different versions, and there’s sorting through all the original orchestrations. But to be able to restore a score and hear it as it was originally intended, to me, is our mission.Tell me more about the different versions of this score. The one from its out-of-town tryout is very different from the Broadway score, and it has since changed even further.It’s very exciting to go back generally and look at these great pieces that were created, and understand, from a newer perspective, how that might’ve happened, how those people might’ve been in the room together, how they were struggling out of town to find the right opening number. We have someone on the staff here at City Center, Josh Clayton, who’s sort of like a score restoration guru.My study of this has led me to believe that Herman’s original intention was to write a smaller piece. But because of “Hello, Dolly!” and “Mame” and then adding “Dear World” to the canon and all of them running on Broadway at the same time — I also love, by the way, that all of them celebrate a fantastically strong woman at their center — the process was very fraught for “Dear World.” It went through, perhaps, an internal struggle of what they wanted it to be, and it went through some real trials and tribulations.So what version of the score did you end up with?The most important thing was: Let’s pick the version that supports a 28-piece orchestra. And so, we’ve really centered that in our debates and decisions about the different versions that exist. I think we read maybe 10 different scripts in the process. It’s been an enormous research project that I think not every Encores! production will be.What are the characteristics of Jerry Herman’s sound world?The chord progressions he uses and the way he uses voice leading is really distinctive. What I love about the orchestrations in Jerry Herman’s scores is that you can really hear how the brass are brilliantly used for storytelling; they provide such lush power. And with big string sections — when you hear a Jerry Herman song in its original, full orchestration, you’re, like, That’s a Jerry Herman song.This is not his best-known score, but the melodies are stunning. There’s a beautiful song at the end of the show, “And I Was Beautiful,” which I think is a gem that people don’t necessarily know. And what I love about that song is that it is foreshadowed through the entire score in a way that you don’t normally get. Normally, you have a song, and then you have reprises after it’s been introduced. This is the one song that gets foreshadowed for the entire score in underscoring. So, by the time you get to it, it’s like a warm bath.A lot of people will probably come to this more familiar with “Hello, Dolly!,” “Mame” or “La Cage.” How would you prepare audience members who know Jerry Herman for the hits?It’s quintessential Jerry Herman, but it also has European influence. And it has atonal influence. You can tell he was branching into some other territories. So, I think if you love Jerry Herman, you will love this score, but you will also be surprised by it in a positive way. More