Despite its cheerful title, Merrily We Roll Along has the most troubled history of any Stephen Sondheim musical. But a few minutes into the production at Washington's Kennedy Center, it's clear that, two decades after its disastrous Broadway debut, this oft-revised musical is rolling along its smoothest course yet.

It's also clear that, a few cavils aside, the quality of the center's Sondheim Celebration continues to astonish. Two-thirds of the way into this festival, it seems safe to say there's no better place in America for serious musical theater audiences to be spending the summer.

A number of individual scenes shine in director Christopher Ashley's production of Merrily - chief among them, a neuroses-fueled, tour-de-force solo by Raul Esparza that stops the show halfway through the first act. But the production's greatest strength is the way it comes together as a whole.

Based on George S. Kaufman and Moss Hart's 1934 reverse-action play of the same name, Merrily is a musical that has always struggled with its own complex, topsy-turvy structure. The plot moves backward from 1976, when the three protagonists' hopes are long gone, all the way back to the optimistic moment in 1957 when they first met. Even Sondheim's unusually catchy songs are structured in a kind of inside-out manner, with, for example, a second-act song being reprised in the first act.

The problem faced by Sondheim and librettist George Furth wasn't just one of clarity, however. Equally tricky was the task of winning audience sympathy for characters who, when first seen, are bitter (in the case of Mary, an alcoholic novelist-turned-drama critic), angry (in the case of Charley, a playwright/lyricist) and spineless (in the case of Frank, a composer-turned-Hollywood producer).

As we discover, these three were once best friends; Frank and Charley even wrote a splashy hit Broadway musical together. Director Ashley and choreographer Karma Camp cleverly acknowledge Frank and Charley's musical comedy roots in their staging of the opening number, which happens to be the title song. The number is presented with the cast grouped around four pianos that, quite literally, "roll along" the stage.

The effect is more than a reference to the friends' musical comedy background. It also establishes a firm foundation for the entire production. Although Sondheim's lyrics ask dark, central questions - "How can you get so far off the track?" "How can you let it slip out of gear?" - the opening song bubbles with joy and camaraderie, the same feelings that nurtured the friendship of the central characters. Snippets of the title song pop up each time the action steps farther back in time, and the poignance is increased by our recollection of the ebullient imagery with which it began.

It's indicative of the effectiveness of the Kennedy Center production that two of the other standout numbers are intricate songs that demonstrate the creative process while also advancing the plot.

The first is "Franklin Shepard, Inc.," Esparza's lacerating show-stopper. Esparza, who played the equally intense, but humorless, Georges Seurat in the Sondheim Celebration's Sunday in the Park with George, proves a master of comic timing and rapid-fire delivery as he fast-forwards through a crash course in songwriting, complete with rat-a-tat-tatting typewriter and piano keys and even a few harried phone calls.

The staging of the youthful second-act number, "Opening Doors," is also inspired. Cutting up as gleefully as Donald O'Connor, Gene Kelly and Debbie Reynolds in Singin' in the Rain, Esparza's Charley, Michael Hayden's Frank and Miriam Shor's Mary kick up their heels as they go from being unknowns to collaborating on the revue that launches their careers.

Boyish Hayden portrays Frank as a man too easily swayed to be truly sympathetic, though his weakness earns him a degree of pity and understanding. Part of this stems from Shor's ability to let us see Frank through Mary's hopelessly lovestruck eyes. While Hayden's pliable Frank is a man addicted to fame, Shor's acid-tongued Mary is a woman whose one taste of success left her stymied. Only Esparza's nervous and easily rattled Charley is unwilling to compromise his artistic principles, and it costs him his friendship with Frank.

In supporting roles, Anastasia Barzee imbues Frank's first wife with a broad spectrum of emotions in a single song, "Not A Day Goes By," initially sung with sardonic regret when she is divorcing Frank, and later sung tenderly as part of her marriage vows. In the role of Frank's second wife, an ambitious diva, Emily Skinner has some trouble moving beyond stereotype. But Adam Heller brings real heart to the role of the producer husband she forsakes for Frank. Additional kudos go to 10-year-old Justin Pereira, who delivers a crisp 11th hour solo as Frank Jr.

Derek McLane's functional set is augmented with slides by Michael Clark. Especially evocative are the baby pictures that are projected during the overture and conclude with a picture of young Frank, Charley and Mary seated on a roof. Incorporating slides of babies isn't new; a similar device was part of the 1994 off-Broadway production whose revised text and score are used here. Retaining this concept, however, is a wise choice since the hope and promise that the baby pictures represent helps underscore the themes of disillusionment and loss of innocence that surface as soon as the action begins.

"Musicals are popular. They're a great way to state important ideas. Ideas that could make a difference," Frank tells Charley when he tries to persuade him to collaborate on a musical. Merrily We Roll Along has always had important things to say about the dangers of fame, of selling out and of sacrificing integrity.

But the show has also presented some of the most unruly challenges in the Sondheim canon. Continuing its string of celebratory successes, the Kennedy Center has met the show's challenges and given it the important production it deserves.

Merrily We Roll Along

Where: Kennedy Center, 2700 F St. N.W., Washington

When: 7:30 p.m. July 25 and 26, 2 p.m. and 7:30 p.m. July 28; in repertory through Aug. 24

Tickets: $20-$79

Call: 800-444-1324