"A Private Battle," on CBS (Channel 9) at 9 tonight is another entry in what appears to be a tear-jerker sweepstakes on television this season. It is the story of writer Cornelius Ryan's ultimately unsuccessful struggle with prostate cancer, and as a tear-jerker it is neither very good nor very bad.

The promotional spots for this two-hour program must be noted for their remarkable inaccuracy, screeching as they do about a wife who can't cope with the pressure of her husband's illness, the son who's into drugs and the daughter who runs away.

The wife, Kathryn Ryan, as played by Anne Jackson, is rather chubby but certainly copes quite well. The son is no more sullen or stoned than the average American teen-ager, and hey, like, gets his head together by the end of the film. And the daughter runs away for precisely one night.

Ryan, the best-selling author of "The Longest Day," "The Last Battle" and "A Bridge Too Far," was 50 when he found he had cancer in 1970. A journalist by trade, he decided to research his illness as he would a book, and recorded his thoughts about the illness on tapes that were discovered after his death in 1974. His wife, using these tapes, put together a book five years later, and it is on this book that the television movie is based.

Jack Warden as Ryan seems most uncomfortable during the taping scenes, in which he is talking about death into a microphone. The taping was evidently used as a device to let the audience know what Ryan's thoughts are, but somehow it looks silly.

The film is too episodic to present a point of view effectively or even to present a point. It starts out seeming to be about how stupid and callous doctors can be in their relations with seriously ill patients, and how "experts" offer conflicting advice. Then the script wanders into the father-son confrontation over a marijuana crisis.

People start talking about how courageous Ryan is in dealing with his illness, but the ways in which he is courageous are not made very clear to the viewer. Suddenly there he is conducting an amateur production of "Finian's Rainbow," and then there's a news clip of Walter Cronkite announcing the real Ryan's death. A very clean, un-messy, Hollywood way to go. The trumpets are playing one minute and Uncle Walter is mourning you the next.