`Good Mother': the film is as controversial as the book

``The Good Mother'' is a breakthrough film: the first big-star, big-director Hollywood production to deal with the difficult subject of childhood sexual abuse. The star is Diane Keaton, and the director is Leonard Nimoy, of ``Star Trek'' fame. They make a sincere effort to raise tough questions - about everything from sexual permissiveness to the role of courts in determining how families should live. Unfortunately, the film makes questionable decisions that weaken its impact. The main character is Anna, a working woman who's divorced, gets along fine with her ex-husband, and happily orders her life around Molly, her young daughter. She admits she's no overachiever when it comes to building a career outside the home. But she feels there's no more needed or honorable profession than raising a child in a warm and secure household.

When she falls in love with a new boyfriend, a sculptor named Leo, she welcomes him into the household and encourages his friendship to her daughter. Her happiness caves in when her former husband slaps her with a child-custody suit, claiming that Leo has sexually abused Molly and that Anna irresponsibly allowed this to happen. The movie then becomes a courtroom drama, with Anna struggling to keep her daughter - even though she knows there's a degree of truth to the charges.

``The Good Mother'' rarely sensationalizes its delicate subject. The screenplay emphasizes how important the sexual dimension is in Anna's relationship with Leo, and there are a couple of surprisingly graphic sex scenes. But the episodes dealing with the film's main concern - the alleged abuse of Molly, and Anna's battle with the court over custody - are tactfully handled.

And in a way, that's the trouble with the movie. ``The Good Mother'' is about child abuse - a family and social problem that most people find repellent just to think about and that generates controversy even among experts who try to define it and find solutions. It should make audiences squirm with discomfort at the hard facts and dilemmas it raises.

But that wouldn't sell many tickets at the box office; so the film works inordinately hard at being tasteful. In doing this, it ends up dodging the most difficult aspects of its subject. It stays on the surface of one concern it brings up, the proper degree of openness in teaching a child about sex. It fails to resolve the tensions that develop between the main adult characters. And more important, the child abuse itself turns out to be so ambiguous that some people would hesitate to call it abuse at all.

The movie is so eager to keep its audience comfortable that it won't even let the Keaton character have too many hardships. Every time she needs money or comfort, there's a set of wealthy grandparents (Ralph Bellamy and Teresa Wright) who don't need much coaxing to help her out.

Mr. Nimoy has slickly directed ``The Good Mother,'' and David Watkin has prettily photographed it. Miss Keaton and Liam Neeson are convincing in the main roles, and such gifted people as Jason Robards and Joe Morton show up in supporting parts.

Yet the professionalism of ``The Good Mother'' doesn't save it from a common pitfall of ``message movies'' that want - but don't quite have the nerve - to confront genuinely troubling concerns with courage and candor.