In a program note for his play "Somewhere" at TheatreWorks, playwright Matthew Lopez says the characters aren't based on his family but "based on my love for my family," and that's a defining quality of this warmhearted drama.

If you could distill American drama down to two themes, they might be family and dreams, especially if dreams can also encompass delusions. Lopez's play, which had its premiere last fall at San Diego's Old Globe and has been seriously revised for its bow in Mountain View, is all about a family of dreamers.

"We force the world to look like our dreams," the starry-eyed mother tells her disillusioned son. "We do not force our dreams to look like the world."

That's the truth. How else to account for just how happy the Candelarias are when the reality of their situation could make for a depressing evening of theater. An immigrant family from Puerto Rico, they live in a tenement on New York's Upper West Side. Dad is nowhere to be seen, except occasionally in letters from distant places, so it falls to oldest son Alejandro (Michael Rosen) to be the man of the house.

His mother, the sparky Inez (Priscilla Lopez, the playwright's aunt), works odd jobs so her talented kids can take acting and dancing lessons. Her eldest even has the claim to fame that he was a kid actor in "The King and I" opposite Yul Brynner. Mom is in thrall to musical theater, and how could she not be? She's living blocks above Times Square at the end of what would come to be known as the Golden Age of the Broadway musical.

She ushers by day and is a nightclub hostess by night. Her current stage obsession is "West Side Story," even though there are so few actual Puerto Ricans playing the Puerto Rican gang members. The entire family follows mom's lead and worships at the shrine of musical theater, playing cast albums non-stop and dancing up a storm, mostly for each other's amusement.

When the Candelarias connect, it's usually when they're dancing along to a show tune. Early in Act 1, with the pas de deux music from "West Side Story" playing, Inez dances with Alejandro, and there's just no denying the emotional power of watching a son dancing beautifully and tenderly with his mother.

But it's not all show tunes in the apartment. Alejandro, who's in his early 20s, has given up his Broadway dreams because he spends so much time working to put food on the family table. Younger brother Francisco (Eddie Gutierrez) is obsessed with becoming a movie actor, and youngest child Rebecca (Michelle Cabinian) is anxiously awaiting her turn in the spotlight.

Just when you think the Candelarias are delusional and their musical fantasies will get the better of them, in waltzes the real possibility of showbiz glory in the form of Jamie (Leo Ash Evens), a neighborhood boy who practically grew up with the Candelarias. Jamie is now assistant to Jerome Robbins, a Broadway legend and the director of "West Side Story" on stage; Robbins is soon to co-direct the motion picture.

Of course Inez wants all her talented children in the movie, but there's just one problem. The City of New York is evicting them. Their building is about to be torn down to make way for Lincoln Center.

Watching the Candelarias strive for things that seem way out of reach and help each other maintain their dreams/delusions calls to mind other plays about families, most notably "The Glass Menagerie," "Death of a Salesman" and, appropriately for this family, "Gypsy." There's even a potential gentleman caller in Act 2 who may or may not be coming to dinner.

Director Giovanna Sardelli strives for a realistic tone and rhythm to the often rambunctious family life, and then contrasts that with lovely flights of fantasy when the characters dance into an altered, often euphoric state. She and Lopez rely on those flights a bit too much, so they lose some impact, even when they're beautifully performed (the music is recorded and the choreography is by Greg Graham).

She gets strong performances from her cast, and Lopez, a member of the original Broadway cast of "A Chorus Line" and a Tony Award winner, dominates the stage in a role inspired by her own mother (whose maiden name happened to be Candelaria). As effective as Lopez is, she is nearly upstaged by Rosen's Alejandro, a soulful young man whose sense of responsibility only barely outpaces his desire to dance. And to dream.

While it's easy to set up dreamers and squash them with a mighty blow of reality, playwright Lopez is more compassionate with his characters. There could be more grit and less gloss in this story, but ultimately it's not sappy.

There's a certain degree of real-world grimness puncturing the show-tune delirium, especially in Act 2, but there are also small, deeply felt triumphs and acts of tenderness that keep hope alive and root the family's happiness in each other rather than in pipe dreams. That really makes "Somewhere" something.

What: "Somewhere" by Matthew Lopez, presented by TheatreWorks

Where: Mountain View Center for the Performing Arts, 500 Castro St.

When: Through Feb. 10, with shows at 7:30 p.m. Tuesdays and Wednesdays, 8 p.m. Thursdays and Fridays, 2 and 8 p.m. Saturdays, and 2 and 7 p.m. Sundays

Cost: Tickets are $23-$73, with discounts for students, seniors and educators.

Info: Go to theatreworks.org or call 650-463-1960.