THE PIANOS are the real thing. The two glorious Yamaha concert grands at the Geary Theater for ACT's production of "2 Pianos 4 Hands" are so long their sleek, gleaming, black bodies placed not quite end-to-end stretch almost all the way across the stage.

The four hands are the real thing, too. Though they're not the hands that created the show and have been principally responsible for its widespread success. The fingers of Gregory Charles and Jean Marchand fly over the keyboards in brightly phrased bits - some short, some long - of Bach, Beethoven and Mozart; Schumann and Schubert; Grieg, Rachmaninoff and Chopin; Richard Rodgers, Vince Guaraldi, John Lennon and Billy Joel.

The faces and voices connected to those fingers do some engaging work, as well. As seen at Tuesday's final preview ("2 Pianos" opened Wednesday), Ted Dykstra and Richard Greenblatt's semi-autobiographical concert-play, about the perils and pitfalls of studying to become professional musicians and not quite making it, looks as if it's, well . . . in good hands.

The music is pleasantly and, for the most part, well-performed. Charles and Marchand are also engaging actors who inhabit the many characters - the young piano students, from about ages 10 to 35, and a variety of comically idiosyncratic teachers and imposing conservatory examiners - with easy grace. The 90-minute one act exerts its gentle charm and achieves a poignant resonance in a minor key as each young man is made aware how far his musical skills fall short of his concert aspirations.

The 90-minute version, by the way, is the shortened form created for non-Canadian audiences. Dykstra and Greenblatt, professional actors in Canada who had started to be concert pianists, opened "2 Pianos" in Toronto in 1996. They've been touring with it ever since, with successful runs across Canada, Off Broadway and, most recently, in London.

They've also created spinoff companies, allowing them the freedom to resume their regular stage, film and TV careers. Marchand and Charles opened in the French Canadian version, "Deux Pianos, Quatre Mains," in Montreal two years ago (the ACT production is their English-language debut with the show), and another version - with two women at the keyboards - is touring the States. Dykstra, who directed ACT's production, is heading for Australia to stage it yet again.

Lean, bald Marchand, who plays Richard (as in, Greenblatt), is the more seasoned and accomplished actor of the two. Bespectacled, self-described "African Canadian" Charles (Ted), who's had more of a career as a musician and radio and TV host, is a little less certain in some of his characterizations. Both are adept at the piano, lending automatic credence to their characters' musical ambitions.

It's a story that anybody who seriously studied

a musical instrument as a child immediately will relate to - as well as all those who've unsuccessfully tried their hand at any endeavor (which probably includes most of us). Charles and Marchand open with a deft, quick-fingered, four-hand foray into Bach's D Minor Piano Concerto (to which they return, more masterfully, at the end). The piece dissolves in muffed notes and flubbed runs.

Suddenly, they're children, running basic - then not-so-basic - scales. They alternate as the child and then teen students, and as a variety of teachers and parents, playing clever variations on the adult idiosyncracies with which children have to learn to cope. They're delightfully stymied, eager-to-please and easily distracted as they cope with the problems of standard introductory problems ("What key are we in, Richard?" "What's the time signature of this piece?").

One teacher after another flies by: the nun with the splitting headache (Charles) who slips away from each lesson for "a little lie-down"; the Frenchman (Marchand) who explains technique in terms of seduction ("When you make love to a woman, do you use only one hand?" he asks the dumbfounded young Ted); the Italian who teaches manly arpeggios lying on the floor. So, too, do parental confrontations, with Marchand particularly effective as a teen rebelling against his father's tutorial advice, and Charles trying to convince his dad that he doesn't need good academic grades to get into a conservatory.

Snatches of practice pieces fly by as well, as the two teen pianists bedevil each other through Mozart's Duet in D Major or come a cropper trying to master a passage from Chopin. Dykstra keeps the staging beautifully simple, on Chuck Sanger's attractive set of large frames, lit in pleasing pastel tints and graced with occasional title and score-notation projections by Derek Duarte. There's nothing particularly deep or compelling in the story, or inventive in either the characterizations or details. We know pretty well what's going to happen. But when it does, the climax is nicely laid out. Charles' Ted reaches his crisis in a conservatory audition with Schubert's A-flat Impromptu. Marchand's blisteringly accurate critique is met with affecting devastation.

Marchand's Richard gets his comeuppance at a jazz academy, trying out with a dexterous, overly ornate "My Funny Valentine" that earns an appropriately scathing rebuke from Charles' instructor. Charles is hilarious, as well, as an obnoxious drunk in the piano bar where we next see Richard, making a living playing Billy Joel's "Piano Man."

The lesson is driven home in Charles and Marchand's response to a brief recorded bit of Vladimir Horowitz's rendition of Liszt's "Mephisto Waltz." The stunning mastery and seemingly effortless lightness of Horowitz is an unanswerable argument about how far Ted and Richard fall short of reaching their goals. And yet, the pleasures conveyed by many of their own renditions, including the four-handed Bach that closes "2 Pianos," is equally convincing of the worth of musicianship that's less than virtuosic. Stick around for the encore. The sheer joy of Charles and Marchand's duet on Scott Joplin's "Maple Leaf Rag" (a Canadian-American connection) is well worth the wait.