The most exciting part of any production of "Oklahoma!" is the ensemble performance of the rousing title song, and C.A.S.T. in McLean does it with all the power and gusto that unforgettable climactic tune demands.

The rest of the troupe's "Oklahoma!" is O.K., too.

C.A.S.T. (an acronym for Community Alliance Supporting Theatre) is taking on the great Broadway war horse for its season finale and as part of its newfound commitment to perform only musicals--or what company President Kevin D. McCormack calls "worthy musical plays."

The classic 1943 Rodgers and Hammerstein show, the prolific team's first collaboration (originally titled "Away We Go!"), certainly fills the bill. Based on a play, "Green Grow the Lilacs," by Lynn Riggs, the show is credited with changing the direction of Broadway musicals, which often were merely showcases for new songs or for famous singers. "Oklahoma!" put story and character first and allowed the songs to advance the plot and reveal personalities.

The original Broadway cast album became one of the first best-seller soundtracks of a stage show. And, in 1955, "Oklahoma!" was transformed into a popular Hollywood film, starring Gordon MacRae and Shirley Jones.

Despite some flaws in the C.A.S.T. production, McCormack handles his task with respect for the integrity of the show, preserving all of the original songs and allowing three full hours to tell its tale, with an impressive 33-member ensemble.

Set at the turn of the century, the show is mainly a story of love between a cowboy, Curly (Travis Corker), and a farm girl, Laurey (Mary Davis), who is being stalked by a surly farmhand, Jud Fry (Michael F. Hoskinson).

Corker's Curly is a wonderfully brash and folksy cowboy who is easy to cheer for. And the packed house on Saturday night did plenty of that. Corker belts out Curly's tunes ("Oh, What A Beautiful Mornin' " and "The Surry With the Fringe on Top") with enthusiasm, and he's fun to hear, even when he stretches for the high notes.

Davis joins him in a fine duet in "People Will Say We're in Love." Davis offered stellar performances in a McLean Theatre Alliance production of "Blame It on the Movies" and in Little Theatre of Alexandria's recent "Stardust." Her take on Laurey seems a bit too refined at times, but Laurey's character is not a strong feature of the show.

The audience Saturday warmed up most apparently to the comic characters. Randall Jones does a grandly hammy turn as Will Parker, a cowpoke who is nuts about Ado Annie, played beautifully close to the top by Tammy Roberts. And Scott Kyriakakis got a big hand for his clownish performance as Ali Hakim, a peddler/con man.

Hoskinson's Jud is so sleazy, the audience didn't know whether to cheer or jeer at the curtain call.

Even with all this talent, there are flat spots in the production. Awkward moments occur mainly in getting people on and off the stage, which creates a sort of disjointed quality, particularly in the first act. In one instance, a duet ends abruptly when a crowd rushes from upstage and begins crooning another tune. Several times, the curtain is drawn for long set changes that don't seem all that necessary in the end.

Choreographer Pamela McCormack (wife of director Kevin McCormack) has engineered some memorable and clever dance numbers. But dancing and singing are sometimes obscured by shaky notes from a 13-piece orchestra conducted by James Gibson.

Still, nothing can detract from numerous individual performances, or from that astounding show stopper, "O-o-o-o-o-O-klahoma! Where the wind comes sweeping down the plain." See? You can't get it out of your head.

"Oklahoma!" continues at 8 p.m. Friday, Saturday and July 30 and 31; and 2 p.m. Sunday, at the Alden Theatre of the McLean Community Center, 1234 Ingleside Ave., McLean. Tickets are $12.50; $1 discount for McLean residents, students and senior citizens. Call 703-790-9223 for information; 202-432-7328, for reservations.