If there were such a place as Sondheim University, Eric Schaeffer would be entitled to a tenured faculty job. Over the past decade or so, he's established himself as one of the premier guardians of Stephen Sondheim's legacy, a role he cemented last summer with his stewardship of the Kennedy Center's highly accomplished Sondheim Celebration.

Schaeffer has directed revivals of many of the works in the "canon" and even staged one of those ubiquitous Sondheim anthology shows, which went to Broadway. But he had never tackled "Follies," the gorgeous 1971 pastiche that many lovers of Sondheim's work believe is his greatest. It is also perhaps the most challenging to stage. Set at a reunion of ex-Follies girls, the musical complexly weaves the story of two disintegrating marriages into an evening of songs that both recall the past glories of the Ziegfeld era and reflect on the current miseries of its faded stars.

"Follies" is in short a bear, a fragile, beautiful one. Some enterprising directors have tried to tame it since the breathtaking original -- overseen by Hal Prince and Michael Bennett -- often with disappointing results. Now, Schaeffer has taken a well-earned crack at the musical. It's sad to say, but the eagerly anticipated production, whose initial run sold out before it opened, is far from the director's best work. This is a weakly cast and irritatingly amateurish incarnation of a show that, when performed satisfyingly, makes a convincing case for musical theater as art.

With a cast of 35 and a 14-piece orchestra, "Follies" is the largest production Schaeffer has ever tried to squeeze into his 136-seat Signature Theatre. While this "Follies" isn't much to look at, the surroundings are not the central problem. The musical traverses a host of themes, from fidelity to self-fulfillment. But fundamentally, it's about the illusions we create, in our lives as well as on the stage. Those illusions are embodied by the apparitions who haunt the reunion, ghostly younger versions of the wrinkled and lumpy ex-showgirls -- the Weismann girls -- around whom the evening is built.

In Schaeffer's wobbly revival, unfortunately, there is little sense of the connection between the older women and the lives they formerly lived. The ghosts of their younger selves may peer out eerily from the margins of the ruined "Weismann Theatre," but it is almost impossible to imagine many of the actresses here as the old pros they are intended to be. Inadvertently, Signature has reinvented the show as the story of the reunion of the gallant former stalwarts of a broken-down community theater.

Reconciling this "Follies" with some of Schaeffer's stellar recent work -- his illuminating, wonderfully acted "Passion" at the Kennedy Center, his emotional, scaled-down "110 in the Shade" at Signature -- is a task unto itself. Both of those productions benefited from expert personnel decisions: Judy Kuhn and Michael Cerveris, for instance, in "Passion"; Jacquelyn Piro and James Moye in "110." What Schaeffer's latest production reinforces is the idea of casting as destiny.

With a few exceptions -- Dana Krueger's elegant Heidi Schiller being one -- the actresses don't carry themselves, or sell their numbers, as if they're former Ziegfeld girls. In Judy Simmons's all-too-carbonated rendition, "Broadway Baby," the score's surefire show-stopper, becomes fodder for a nursing-home romp. Elizabeth van den Berg's version of "Ah, Paris!," performed in the guise of the chanteuse Solange La Fitte, is a shallow cartoon. Donna Migliaccio's lackluster delivery of the usually volcanic "I'm Still Here" vanishes from memory in an instant. And Ilona Urbanski and Steven Cupo are not even remotely persuasive physically as a bygone dance team re-creating their duet, "Rain on the Roof."

If the atmospheric songs don't work -- even the famous mirror number, "Who's That Woman," unfolds like a tacky scene from "The Golden Girls" -- "Follies" collapses on itself as completely as the dilapidated theater in which it is set. The Signature space is not particularly adaptable to the show; working in cramped conditions, set designer Lou Stancari evokes a crumbling theater that feels more like a suffocating cave than a great old vaudeville palace. (Aside from some imaginative contributions in the final scenes, Robert Perdziola's costumes only add to a general sense of gloom.)

Onto the stage wander the former beauties for their reunion, and in the opening minutes, there is a welcome air of occasion. The year is 1971, but the preceding decades are alive in the room as well. Specters of young chorines in tattered gowns and dusty plumage float across the stage, imitating the gestures of the older women. There's decay all around, in the splintering beams, the sunken cheeks, the tattered relationships.

The show's psychological baggage is carried by two couples at the party, the embittered politician Ben (Joseph Dellger) and his wife, Phyllis (Judy McLane), who are rich and miserable, and the hapless salesman Buddy (Harry A. Winter) and his wife, Sally (Florence Lacey), who are middle-class and miserable. As the book by James Goldman would have it, they are self-loathing frauds, mistrusting, unfaithful, unhappy at the way their lives have turned out and unable to face the truth about themselves.

One of the more miraculous aspects of "Follies" is the way in which the elements of music and time are intermingled. Not only are the introspective songs, among them Sally's glorious "In Buddy's Eyes" and Ben and Sally's "Too Many Mornings," interspersed among the nostalgic numbers, but the leading foursome's younger selves are also woven into the narrative, most effectively in the memory song "Waiting for the Girls Upstairs." The mechanics of the numbers have been worked out credibly, but there's little evidence of the songwriter's careful layering when it comes to the characters themselves. Though you're sitting within a few feet of these people, you are rarely given the opportunity to get to know them, to commune with Sally's emotional exhaustion, Buddy's sense of rejection, Phyllis's loneliness, Ben's self-contempt.

McLane's Phyllis comes closest to achieving these aims. She's sleek and cunning and jauntily bitchy in "Could I Leave You?," which may be the best solo of the evening. (Her "Story of Lucy and Jessie," a song that was wrongheadedly replaced in some recent revivals of the show, is also excellent.) With his powerful baritone, Dellger is a decent match for McLane, though his Ben is more a glad-handing party hack than a stuffy politico.

Winter, so pleasing as the father, H.C., in Schaeffer's "110," has a tougher time nailing Buddy, the evening's sad sack; he lacks the clownish instinct for "The God-Why-Don't-You-Love-Me Blues," his comic song in the closing "Loveland" fantasy sequence. And Lacey does not bloom as the tragic Sally. She has problems with the magnificent, demanding torch song "Losing My Mind." From what I could tell, the singers are unamplified, which is a marvelous thing. It was just that the number seemed to be a vocal strain for her.

It's no fun issuing a laundry list of this kind, especially when a company puts its resources behind such a seminal work. But the truth is that Schaeffer does Signature's devoted audiences no favor by throwing such a hot spotlight on many actors who do not belong in mainstage productions at a theater with national aspirations. To borrow a Sondheim phrase, what becomes indelible about this "Follies" is the cornucopia of imperfections.

Follies, music and lyrics by Stephen Sondheim, book by James Goldman. Directed by Eric Schaeffer. Lighting, Chris Lee; costumes, Robert Perdziola; orchestrations, Jonathan Tunick; musical direction, Jon Kalbfleisch; sound, Tony Angelini, choreography, Karma Camp. Approximately 2 hours 30 minutes. With Deanna Harris, Suzanne Briar, Claire Mailhot, Eva Kolig, Joe Peck, A.K. Brink, Tracy Lynn Olivera, Will Gartshore, Sean MacLaughlin. Through June 1 at Signature Theatre, 3806 S. Four Mile Run, Arlington. Call 703-218-6500 or visit www.signature-theatre.org.

Chrystyna Dail, Harry Winter and Eleash Gamble in Signature's creaky production.Joseph Dellger and, especially, Judy McLane, left, provide rare bright moments in Eric Schaeffer's somewhat disappointing rendition of Sondheim's "Follies," at the Signature Theatre.