THEATER REVIEW : An Ode to Modern Living : ‘Falsettos,’ the story of a man who leaves his wife and son to move in with his male lover, enlightens through wit.

Falsetto : An artificially high voice, higher and thinner than a tenor’s, says Webster’s.

“Falsettos”: the quintessential musical for the 1990s, even though its first half is set in 1979 and its second in 1981.

The word and the title connect briefly, as a wry symbol for homosexuality. But “Falsettos,” the musical (its West Coast premiere was at the Old Globe Theatre on Thursday), is also the contraction of titles from what were once two shows--”March of the Falsettos” and “Falsettoland.” Their creators subsequently streamlined these interconnected musicals into one.

So much for the explanation. It doesn’t begin to describe the impact of this stunning William Finn-James Lapine ode to modern living.

The tendency has been to describe “Falsettos” as a musical about homosexuality, which is like saying that “The Merchant of Venice” is a play about money.

“Falsettos” is about the gender-bending and sexual lunges and cross-pollinations that complicate relationships in this last quarter of the 20th Century. It is mostly about compassion, coping, divorce, parenting, being Jewish and learning to understand and work things out.

And, yes, it is also about AIDS and death. Still, the great achievement in this story of Marvin, who leaves his wife, Trina, and son, Jason, to move in with his male lover, Whizzer, lies in its musical verve and life-affirming lyrics. Deceptively simple phrases create complex patterns of humor and candor as complications mount.

One complication is the fact that Marvin’s shrink, Mendel, falls in love with Trina, and that son Jason is highly confused by the escalating whirl of circumstances. All of these lives become inextricably enmeshed, but no sad songs just yet. The first half may end with Marvin and Whizzer’s relationship on the rocks, but Mendel and Trina are off to get married.

Eccentric? Everything about this musical is eccentric. As in the earlier, separate versions of the show, sets are suggested by speeding pieces of furniture that spin by or zoom conveniently into place (the designer is Douglas Stein, with lights by Frances Aronson). Lovers’ quarrels are as apt to be sung during a game of chess as they are during a racquetball set. A bar mitzvah text in Hebrew becomes a lyric, and a ballad like “The Thrill of First Love” doesn’t discriminate: It applies equally to gay, lesbian or heterosexual lovers.

This is enlightenment. It is also wit and great artistry. But any show that kicks off with a song called “Four Jews in a Room Bitching” will shock some people, and if you’re one of them, so be it. The second half of “Falsettos” narrows its focus even more, dealing with the nice lesbians next door, Marvin and Whizzer’s reconciliation and Whizzer’s illness and death. Heavy duty, deeply tender stuff that will rock closed minds and blow open ones away.

The production, staged by Lapine, is as tight and resonant as a drum. He also has a super company and, on opening night, a last-minute replacement in the role of Jason.

Talented sixth-grader Jonathan Kaplan, who created the part on Broadway, stood in for an ailing Ramzi Khalaf, and it’s easy to see why Kaplan received a Tony nomination and Theatre World award. There was not a trace of hesitation or self-consciousness in his Jason--just a plain-spoken kid with smart questions that required tough answers.

Gregg Edelman and Peter Reardon are well matched as the ill-matched Marvin and Whizzer, respectively, Edelman having the neurotic edge and Reardon nonchalantly at ease in his playboy skin. His admission of preference for sex versus love in “The Games I Play” is as much Whizzer’s anthem as “This Had Better Come to a Stop” is Marvin’s, though the latter emotion is shared by virtually everyone in the show at one time or another and makes for a hilarious five-part chorus.

Adam Heller’s Mendel, the all-purpose psychiatrist who’s as full of insecurities and needs as the next guy, humanizes a profession that often suffers from remoteness. But it is Carolee Carmello’s Trina, ex-wife, mother and new wife, confused by all three roles, who stops the show with “I’m Breaking Down.”

The title says it all.

Barbara Marineau as a lesbian doctor and Jessica Molaskey as her homemaker lover show up only in the second half (what was once “Falsettoland”). These roles are as sketchy and expedient as ever--Marineau playing the doctor who eventually cares for Whizzer--but this is a minor glitch in a sea of major accomplishment.

Musical direction by Ben Whiteley and arrangements by Michael Starobin match the high energy of Lapine’s whirring direction.

“Falsettos’ ” virtuosity is in its mastery of the bittersweet--and eventually the tragic--wailing over life’s nasty habit of giving and taking away, but without wasting time on self-pity. Instead, the show makes intricate songs from the sour lemons. And the result is glorious lemonade.

“Falsettos,” Old Globe Theatre, Cassius Carter Centre Stage, Simon Edison Centre for the Performing Arts, Balboa Park. Tuesdays-Saturdays, 8 p.m.; Sundays, 7 p.m.; Saturdays-Sundays, 2 p.m. Ends April 25. $18-$32; (619) 239-2255. Running time: 2 hours, 40 minutes.

Gregg Edelman: Marvin

Peter Reardon: Whizzer

Adam Heller: Mendel

Jonathan Kaplan: Jason

Carolee Carmello: Trina

Barbara Marineau: Charlotte

Jessica Molaskey: Cordelia

Music and lyrics William Finn. Book William Finn, James Lapine. Director James Lapine. Sets Douglas Stein. Lights Frances Aronson. Costumes Ann Hould Ward. Hair design Phyllis Della. Sound Peter J. Fitzgerald. Musical director Ben Whiteley. Musical arrangements Michael Starobin. Production stage manager Robert D. Currie. Stage manager Peter Van Dyke.