As an acting piece, ``Marvin's Room,'' a melodrama laced with dark humor, is quite generous. And why shouldn't it be, with the likes of Meryl Streep, Diane Keaton and Robert De Niro on hand? These old pros are right at home, despite playing characters who are some distance from their usual roles. And each is splendid.

But as a movie, ``Marvin's Room'' has problems, from its awkward staginess to its overly sentimental treatment to the fact that it is by-the-numbers predictable. (In many ways it looks an awful lot like one of those generic made-for-TV disease-of-week movies.)

Oddly enough, Keaton - nominated for a best-actress Oscar - directed a much better film with similar themes a couple of years ago, ``Unstrung Heroes,'' which inexplicably failed at the box office.

Adapted from the late Scott McPherson's very personal play, with a screenplay by McPherson himself and directed by stage veteran Jerry Zaks, the story focuses on the rivalry between two disparate sisters and spends a lot of time contemplating death. (It is intended as a metaphor for the AIDS epidemic.)

Lee (Streep) is tough, independent and more than a little selfish. She left her hometown in Florida some 20 years earlier to make her own way in Ohio and has not been in touch with her ailing father Marvin (Hume Cronyn) or her sister Bessie (Keaton) since.

Now, as a struggling single mother (who doesn't put much effort into raising her kids), Lee is having serious problems with her delinquent teenage son Hank (Leonardo DiCaprio, most recently seen in ``William Shakespeare's Romeo & Juliet'').

Hank lands in a mental institution after burning down their house, and Lee's younger son Charlie (Hal Scardino, of ``The Indian and the Cupboard'') is a withdrawn bookworm.

The sweet, giving Bessie, meanwhile, chose long ago to devote her life to caring for her bedridden father, who she says has been dying for 20 years, ``slowly, so that I won't miss anything.'' She's also watching over her dizzy Aunt Ruth (Gwen Verdon).

The plot kicks in when Bessie places a reluctant phone call to Lee, asking her to come home. It seems Bessie has leukemia and needs a bone marrow donor. Lee grudgingly gets her boys together and makes the trek back to Florida, and the dysfunctional family dynamic begins.

De Niro (who also co-produced the film) has fun in a small, atypical role as a mild-mannered, absent-minded doctor, whose mentally challenged brother (Dan Hedaya) is acting as his receptionist (the latter element is played for laughs, a questionable but nonetheless amusing ploy).