Pat O'Brien has made 110 movies in his 63-year career, and has now packed up his wife Eloise and his daughter Brigid and taken them on the dinner theater circuit in "On Golden Pond," a gentle comedy about getting old.

The results, which can be seen at the Hayloft Dinner Theater in Manassas through May 10, are somewhat mixed. O'Brien himself is convincingly acerbic as the misanthropic Norman Thayer, and equally effective in making us love the old geezer.

Unfortunately, the rest of the production doesn't quite measure up. Eloise O'Brien seems to be underrehearsed, unsure of her lines and so tentative in her business that it is hard to relax and enjoy her character. The production suffers from some dinner-theater neglect: Small details like a letter envelope being unsealed and a telephone whose ring seems to emanate from offstage distract attention from the play.

"On Golden Pond" by Ernest Thompson is one of the more remarkable success stories of recent theater seasons. The play is currently being produced by 150 theaters around the country, according to Hayloft producer Frank Matthews, and is about to be released as a motion picture staring Katharine Hepburn and Henry Fonda.

The story concerns Thayer and his wife Ethel ("Ehtel Thayer," says Norman at one point. "Thoundth like I'm lithping, doethn't it?"), who are starting their 48th summer in a cabin in Maine when the play opens and preparing to leave by its end. Norman, who is approaching 80, is worried about his increasing age and approaching death, a fear he responds to with crusty pronouncements and an increase in his customary bad temper. His spirits are revived by a 14-year-old boy, his daughter's soon-to-be stepson whom he teaches to fish and to read good books.

The play, which had successful run at the Kennedy Center in 1979, gives us the vivid and endearing characters of the Thayers, their daughter and her moodish but good-hearted boyfriend, a California dentist, as well as his foul-mouthed son. But the action goes in its fits and starts, setting up problems and solving them so quickly that the impact is never quite realized. The daughter returns from Europe and almost immediately says to her father that she wants to improve her relationship and "become friends." He says okay and that's that, conflict solved. The boy and Thayer, one a typical illiterate teen-ager, the other a cranky old lover of literature, would seem to be ripe for conflict -- but instead they become immediate pals.

The set by Ed Bourgeois and Joe McGuire (who also play the teen-age boy) makes effective use of the small stage. It is hard, however, to understand the choice to play Muzak between scenes.

Pat, you deserve better.