Elderly people as heroes and heroines, rather than as minor characters of either the cute or the scary variety, should become commonplace if films continue to follow the country's demography. "On Golden Pond," in which Katharine Hepburn and Henry Fonda play a retired couple dealing with annoyances from failing memory to a midlife- crisis daughter, is an interesting start. It's not the first such picture, of course, although others, such as the heart-wrenching "Tell Me a Riddle" starring the late Melvyn Douglas, have not had the success to establish the genre. But there's something timid about the way in which Ernest Thompson has adapted his witty play for the screen version of "On Golden Pond," as if it had to do an extra-hard job to prove itself appealing. The cantankerous professor, Norman Thayer Jr., whose favorite subject of conversation for years has been his impending death, and whose devoted wife is the first to call him "an old poop," is rendered with wonderful acerbity by Fonda. Jane Fonda and Doug McKeon, as his middle-aged daughter and her boyfriend, earnest types whose limited scope make them her father's easy prey, are very funny. But these characterizations have been wrapped in an atmosphere of sentimentality, mostly with the clumsy symbolism of two loons on the lake, represented as a couple making it through the cycles of nature. A loon is also fished out of the lake dead, but as we see a couple again, and loons tend to look alike, it's not clear whether the deceased was a lover of one of the mates or part of the original couple and the survivor has found happiness again. Such are the dangers of anthropomorphism. Another retreat from the sharp quality of the play is that the wife, as played by Hepburn, comes off as an ever-cheerful peacemaker, rather than as Frances Sternhagen played her on the stage: decidedly more upbeat than her husband, but just as strong. A decisive moment in the play was when the mother answered her daughter's retrospective complaints by declaring, "Here we go again. You had a miserable childhood. Your father was overbearing, your mother ignored you. What else is new? Don't you think everyone looks back on their childhood wih some bitterness or regret about something? . . . Life marches by, Chelsea; I suggest you get on with it." It had been a major statement about "getting on" with life. But in Hepburn's tremulous delivery, it is only a plea not to create a family fuss. The character is lovely when she is reveling in the delights of life, but does not convey the point that the elder Thayers, for all their difficulties, were durably built.

ON GOLDEN POND -- At the AMC Carrollton, AMC Skyline, Jenifer Cinema, Laurel Cinema, Roth's Tysons Corner, Showcase Pike, Springfield Mall and Wheaton Plaza.