"Growing Pains," a play about new beginnings, itself marks a fresh initiative for Metromedia Television, the merrily wealthy broadcast group whose ventures into original dramatic programming have been few and, so far, unsuccessful. Metromedia has at times looked as though it were incapable of making anything but money.

But with the broadcast of the play tonight -- at 9 on Channel 5, the Metromedia station in Washington -- the company strikes out in a potentially gratifying direction, although this inaugural presentation of "Metromedia Playhouse" is hardly a fully realized or fully satisfying work. As a production, it is shiny and handsome, taped in vast new studios at Metromedia's WCVB-TV in Boston.

Ralph Waite stars as the father of a 26-year-old retarded woman named Helen, played with teeth-rattling ferocity by Katherine Borowitz. The two have a mutually suffocating relationship, caused in part by the father's sense of guilt. His daughter was brain-damaged as a child in the same fire that killed the girl's mother, and "Poppy," as Helen still calls him, was off on a drunk at the time. Hence the guilt and 20 years on the wagon.

Into this already heavily melodramatic situation comes a 38-year-old widow and pet-store proprietor named Andy, played with a delicate balance of sensitivity and determination by Lisa Richards. She wants to liberate both the father and the daughter, whose interdependence has become pathological, and to cure the father of self-recrimination. After she first encounters the embattled pair together, during a meeting fraught with wayward hysterics, the father tells Andy, "If you walked right out the door, nobody'd blame you." Nobody would, and so she does.

But she comes back -- partly, it would appear, because she loves a challenge. Also because she loves the old dude.

A search for scripts to launch the "Playhouse" led the producers to the original Nelson Clark play, which was then honed and adapted for TV by Jon Lipsky. There is a primitive three-act structure that actually works rather well, and the play appears to have been taped in continuous takes, like the dramas at the tail end of TV's Golden Age, rather than having been edited into coherence in postproduction. There is a palpable sense of theatrical spontaneity to the performances.

But the credits list two directors, a stage director (David Wheeler) and a TV director (William Cosel), and occasionally the two seem more at odds than in harmony. "Playhouse 90" only needed one director. Some scenes, like a last-minute tantrum at the Stepping Stone school for the retarded -- Helen's home-to-be -- look well staged except for the fact that a camera is present; what works on stage may look faintly ludicrous on television. Richards' performance in particular seems to lunge out rather than reach out, while Waite, who dwelled so long on Walton's Mountain, has a better command of effects that work within the restrictive parameters of television.

"I can't watch any more; it's just too painful," Andy says near the end of the play, as father and daughter have one more go-round. Some viewers may feel the same way, but in its final scene the play delivers a note of uplift more subtle than those of your average holiday heartwarmers. Imperfect it is, to say the least, but this first play of an ambitious new series is still encouraging. The announcer in the opening credits calls it "Metromedia Playhouse's Growing Pains." No pain, no growth.