Bringing a tough, astringent wit to a subject too often wrapped in the cozy blanket of sentimentality or cute humor, Tamara Jenkins takes a frank look at the indignities of aging in "The Savages," a black comedy that invites viewers to laugh or at least to smile ruefully at the dying of the light. One of those genre-defying hybrids that are sometimes called dramedies, "The Savages" tiptoes along a particularly fraught emotional tightrope, balancing observant humor and deep sadness with uncommon grace.

Jenkins, whose last movie was the 1998 comedy "Slums of Beverly Hills," once again turns her unblinking, level gaze on family, with none of the dysfunctional affectations or consoling quirks that characterize most indie darlings. Here, her focus is on a brother and a sister who, as somewhat aimless adults, must come to grips with the impending demise of the father who abandoned them as children.

As written and directed by Jenkins, and acted by Laura Linney and Philip Seymour Hoffman (who play siblings Wendy and Jon Savage, respectively), "The Savages" is a wry exercise in truth-telling in the midst of otherwise unspeakable taboos. When Lenny Savage begins to experience the first signs of dementia, Wendy and Jon are roused from what looks like suspended animation. Wendy is working as a temp in Manhattan, applying for grants to finish her play, the "subversive, semi-autobiographical" "Wake Me When It's Over." Jon is teaching college in Buffalo, trying to finish his own book, about playwright Bertolt Brecht.

Each has a wildly different reaction to their father's newfound dependence on them. Wendy, seeking to rewrite the irretrievably broken family story, plays the dutiful daughter, looking into swank assisted-living facilities and feeding her father ginkgo biloba. Jon, true to his own Brechtian ideals, plays the realist, signing Lenny up at a functional nursing home and keeping contact at an expedient minimum.

Meanwhile the combative Lenny, played by Philip Bosco in a shattering, even brave performance as a man dimly aware of his own slipping grip on life, listens as the children he barely knows tussle past the graveyard. For all their differences, Wendy and Jon are a lot alike. They're both cereal-eaters and self-medicators, although Wendy is far more practiced in the art of lying to get what she wants, whether it's to her married lover about the condition of her cervix or to her competitive brother about a Guggenheim fellowship.

Those scenes, like so many others in "The Savages," are small, incisive chamber pieces of abrading agendas, swirling psychodramas and, often, mordantly funny humor. Like "You Can Count on Me," in which Linney also played an adult sibling (opposite Mark Ruffalo), "The Savages" has to do with how habits of the heart are passed down through generations. Unlike that earlier film, this often unsettling glimpse into the messiest parts of living and dying offers little by way of reassurance.

Ironically, Jenkins' unvarnished view of her characters' lives, her refusal to give in to conventional notions of closure or comfort, may limit her movie's appeal to people for whom the Savages' tribulations hit painfully close to home. For those who have just lost a parent, or gone through the wrenching transition of the final move, "The Savages" won't provide an escape as much as grimly underline what they already know too well. But at some point, everyone should see it, if only for the inspiration it offers in how to make a functional whole out of imperfect parts.