Joe Papp, the man who gave Shakespeare a permanent address in Central Park, must have known that this would not be business as usual. A new production of the playwright’s early, unloved comedy “Two Gentlemen of Verona” was on the docket, no doubt more from some sense of obligation than out of any real enthusiasm. As director, Papp had signed on Mel Shapiro, who in turn recruited the playwright John Guare to adapt the script. Galt MacDermot, of “Hair,” would be adding some music.

Leaving these three highly creative and unpredictable co-conspirators in charge, Papp skipped town for a vacation. By the time he returned, preview audiences were cheering a full-fledged American musical comedy that won the Tony Award for Best Musical in 1972.

“He came back and saw a monster,” Mr. Guare recalled recently in the lobby of the Public Theater between rehearsals for the first New York revival of that musical. “And he saw audiences loving it. The show was getting a more visceral response than anything he’d ever put on in the park before.”

Papp, the founding father of Shakespeare in the Park and a director in his own right, must have viewed this triumph with a certain ambivalence. Yes? “Well,” Mr. Guare offered by way of reply, “he never went on vacation during rehearsals again.”

Maybe he should have. The “Two Gentlemen” caper turned out as happily as any chapter in the history of Papp’s Public Theater. After its initial run in the park, the show bounced indoors to the St. James Theater on Broadway for a run of 627 performances. The first commercial transfer ever produced by the nonprofit theater that developed it, “Two Gentlemen” paved the way for “A Chorus Line,” which racked up 6,137 performances on Broadway, subsidizing the Public for nearly 15 years.

Shakespeare’s “Two Gentlemen” has been back in the park since then, but the musical hasn’t. This summer, it returns to the Delacorte Theater as a rediscovered classic, with prospects even a confirmed pessimist would have to call bright. The director this time is Kathleen Marshall, whose sparkling Shakespearean credentials include “Kiss Me, Kate” on Broadway and “Boys From Syracuse” for City Center Encores.

The original “Two Gentlemen” is not the most brilliant constellation in Shakespeare’s heaven, but as far as Mr. Guare is concerned, that was a good thing: “There’s an incredible messiness to ‘Two Gentlemen.’ It’s a ramshackle comedy shot through with ravishing poetry. I felt no compunction pulling it apart and putting it back together. I couldn’t have done that to ‘Twelfth Night’ or ‘As You Like It’ or ‘Midsummer Night’s Dream.’ The very ricketyness of the play gave me the freedom to shore it up.”

Leaving Shakespeare’s language intact, he reduced the text drastically. He corrected inconsistencies in the plot while introducing back-story circumstances (Julia’s pregnancy, for one) to raise the emotional stakes. But the challenges were not solely dramaturgical.

After its initial run in Central Park, the production was scheduled to load onto the Public Theater’s “mobile unit” for a tour of low-rent neighborhoods in the five boroughs. What patience would audiences in the streets have for Shakespeare’s florid, narcissistic displays of courtly sentiment? Where was the connection to the explosive realities of their lives? Across the Pacific, Vietnam was dragging on. At home, tension between the races threatened at any moment to erupt into civil war. “At first,” Mr. Guare recalled, “we thought we would be greeted with machine guns.”

One column in their defensive strategy was casting, beginning with Raul Julia, an unknown at the time (but not for long). “Then,” Mr. Guare said, “we thought, ‘How about getting people from all the neighborhoods we’ll be playing in?’ We weren’t going to be isolated in a theater. We felt an obligation to the people we’d be playing to. They’d look up and say, ‘Oh! That’s me!'”

Featured parts were played by an Irishman, a Chinese-American, a Jew, and a Russian-Danish girl. The chorus, Mr. Guare remembered, was “every color under the sun.” (For the record, it also featured future celebrities – actors named Stockard Channing and Jeff Goldblum, as well as Christopher Alden, who went on to renown as a director.)

“And it turned out to be an ecstatic experience,” Mr. Guare said. “People had never heard Latinos speaking Shakespeare before, in a cast with Afro-Americans.” But don’t discount the felicity of the adaptation.

The songs were the solution to a practical necessity. “The point was to put the idea of the dialogue in the air,” Mr. Guare said, “like supertitles before there were supertitles. So people would understand what was to come.” From nine songs at the start of rehearsals, the score grew to some three-dozen musical numbers. Frankly color-conscious, Mr. MacDermot gave the songs inflections of all sorts – Latin, R&B, country & western, Caribbean, you name it – to suit the actors who would sing them.

As one of his song texts, Mr. Guare of course used “Who Is Silvia?” a graceful lyric from the play that has made its way into anthologies beyond number. The rest were unabashedly contemporary – many dashed in the subway – and made no attempt to mimic Shakespeare’s style. The comparison to supertitles hardly does them justice. They’re telegrams straight from the heart. The words aren’t fancy. None are wasted, and the syntax is spare. Yet the sentiments are by turns whimsical, disarming, hip, cool, dopey, or flamboyantly romantic, sometimes all at once.

That’s the case in “Symphony,” which builds from conversational gallantries to an ecstatic anthem in a mere two and a half minutes. A tongue-tied Proteus is proposing to immortalize Julia in some great work of art (a symphony, a book, a statue), presupposing her assurance of undying love (“I wouldn’t want to make you immortal,” he helpfully explains, “unless you agree to this condition”). Raul Julia, a technically challenged vocalist but blessed with a sound of seductive richness, delivered the song partly in snarls, partly in caresses, conjuring up a born Don Juan. There was satire of a sort, too, as when the warmongering Duke of Milan, parroting Richard Nixon, vowed – if re-elected – to “Bring All the Boys Back Home.”

Unlike the original creative team, who could go at Shakespeare’s Elizabethan antique with a virtually unfettered hand, Ms. Marshall is bound by the solutions they came up with. At this remove, “Two Gentlemen: The Musical” is unmistakably an artifact of the 1970s. Though she never saw the original production, the score has haunted her since her teens.

“I listened to the songs all the time,” she said. “And I saw it in a little barn called the Odd Chair Playhouse in Pittsburgh, where my brother was an apprentice, working sound.” (That would be the star choreographer-director Rob Marshall, Oscar-nominated for “Chicago,” and, like his sister, a frequent Tony nominee.) “It’s so perfect to bring the show back to the park. You can feel it was created for that environment. I can’t wait to hear songs sung outside to the night air.”

Oscar Isaac, whose training at the Juilliard drama division came to a close this spring with his charged performances as Macbeth, plays the devious, two-timing Proteus, the part originated by the charismatic Julia, a fellow Latino. Graduating from drama school with a contract in one’s pocket is a fine thing, and Mr. Isaac had one – for the new Nilo Cruz play “Beauty of the Father” at Manhattan Theater Club this fall. After graduation, with the interim still on his hands, he tried out for “Two Gentlemen” and got lucky again.

“Oscar was a revelation to me when he auditioned,” Ms. Marshall said one afternoon after rehearsals in the studio downtown. “It’s so exciting to be introducing him to the New York audience, and the others, too.” She is not alone in her enthusiasm. Before the production moved to the Delacorte, Mr. Isaac strolled up to the park with Rosario Dawson to get a feel for the house. With two dozen movies to her credit (from “Kids” to the forthcoming “Rent,” in which she stars as Mimi), Ms. Dawson is onboard for her stage debut as Julia, the mistress Proteus betrays.

“We’re really chugging along,” Mr. Isaac reported, effervescent on the phone. “We looked at the set, and I felt, ‘Oh my gosh! We’re ready to go! Bring ’em in!’ Shakespeare is all about the connection with the audience, looking at the people who are looking at you, and saying, ‘I’ve got a story to tell you. Come with me. I know you’re with me even if I do a bad thing.’ For my first show out of school to be Shakespeare, sort of, is awesome. This show adds things, spices it up, brings in some unique stuff. It’s still the real play.”

Joyous as the show is and was meant to be, the Vietnam War cast its shadow across the festivities. No need to spell out the parallel today. “It’s eerie,” Ms. Marshall reflected, “how ‘Bring All the Boys Back Home’ resonates. Here we are, 34 years later, and now our boys – our boys and girls – are overseas again. We’ve come full circle.”

Until September 11 (entrance to Central Park at 81st Street and Central Park West, 212-260-2400).