Movies that take their titles from famous songs don’t have a very good track record (if you’ll pardon the pun), and this one is no exception to the rule. In “Something’s Gotta Give,” writer-director Nancy Meyers, who milked sitcom-quality gags about male-female relationships for much more than they were worth in “What Women Want” (but scored big in the process), returns to pretty much the same territory here. This time, however, she adds an ageist element to the sexist mix: the romantic entanglements involve two fifty-plus people, Harry (Jack Nicholson) and Erica (Diane Keaton), and two thirty-something ones, Julian (Keanu Reeves) and Marin (Amanda Peet), in a variety of supposedly bittersweet, humorous reversals. If we’re lucky, audiences will feel that the well has run pretty dry, but Meyer might strike paydirt again; unfortunately, fools’ gold is often enough to attract lots of eyes.

As the picture opens, Harry Sanborn (Nicholson), a sixty-three year old inveterate Lothario, is driving his latest young squeeze, Marin (Peet) to her mother’s Hampton beach house for a weekend tryst. After they arrive, though, they’re surprised to learn that mom Erica (Keaton), an uptight divorcee and highly regarded playwright, is there with her college prof sister Zoe (Frances McDormand, pretty much wasted in the kind of wisecracking second-banana role that would once have been played by Eve Arden or Ann Sothern); the initial encounter is predictably cute. Despite some tension, especially between Harry and Erica, all four decide to stay on. But Harry suffers a mild heart attack just as he and Marin begin their bedroom antics, and he’s soon hospitalized–bringing the group into contact with Julian Mercer (Reeves), a doctor who’s smitten with Erica’s work as well as the writer herself. In one of those utterly implausible twists that badly-written stuff like this inevitably takes, Harry and Erica are soon sharing the house alone while he recuperates, and they find themselves astonished to be attracted to one another. Marin, meanwhile, has moved on elsewhere (in a singularly unamusing plot development, her main cause of concern becomes her father’s engagement to a woman her own age) and Zoe has disappeared (presumably going back to campus?). But Julian pops in periodically to treat Harry or swoon over Erica–-a role that Reeves tries to enact with cool dignity, failing in the process.

But the spotlight is definitely on the two oldsters. Nicholson does his cantankerous shtick for two hours, putting those famous eyebrows and that lascivious smirk into overdrive to sell material that’s decidedly second-rate (especially when it turns stickily sentimental). Keaton, on the other hand, is all tics and mannerisms, going into paroxysms of embarrassed dithering at the drop of a hat and at one point even suffering through a prolonged crying jag that turns her into a wailing banshee. It’s especially disheartening when the two are forced to reveal more of their anatomies than any self-respecting viewer will want to see for the sake of some “naughty” humor designed to appeal to the older audiences the picture is obviously aimed at. Glimpsing Jack’s derriere and Diane’s bosom isn’t exactly the equivalent of looking straight into the sun, but the experience still isn’t a pleasant one. It’s also curious that a woman director would choose so often to focus her camera, especially in the early part of the picture, on the undulating, tightly-packed backsides of young women. One might expect this of a drooling male helmer, but here the effect is more than a trifle surprising.

Most of “Something’s Gotta Give,” of course, is devoted to devices to prevent the inevitable final clinch between Harry and Erica–especially the old fellow’s persistent inability to commit–and one expects that. One might well ask, however, for a little imagination in contriving them–something that’s painfully lacking here. (The repeated business of having Harry suffer what he takes to be heart attacks as he stresses out over his situation is especially lame, not to mention a bit distasteful. And it’s used so often that maybe the character should have been named Sanford in deference to Redd Foxx.) But the worst thing about “Something’s Gotta Give” is that after feeding us this prefabricated pablum for ninety minutes, Meyers has Erica–who’s been described as a serious playwright, the most impressive female practitioner of the art since Lillian Hellman–turn what we’re just seen into her newest opus. And not only does its first reader, the lanky Julian, declare it to be “sweet, smart and funny–the best thing you’ve ever done,” but it becomes an instant Broadway smash. It takes real chutzpah for a writer-director to characterize what’s really her own movie in that way, especially when such descriptions are so richly undeserved.

Of course, that’s not enough for Meyers. She has to prolong the agony still further by keeping Harry and Erica apart for another twenty minutes until she can contrive a final laughter-and-tears reunion for them in a place telegraphed much earlier. It’s an attempt to create the same sort of supposed magic that marked the finales of “An Affair to Remember” and “Sleepless in Seattle,” but in this case the result comes across as even more cloying and manipulative. And though it’s bad enough for Nicholson and Keaton, the episode is worse for poor Reeves, who once again must play the smiling doormat.

The moral of all this is simple: If you want to see Jack Nicholson acting his age, rent “About Schmidt.” And if you’re crazy for Keaton, stick with “Annie Hall.” The stars may be acting royalty, but their joint vehicle is the cinematic equivalent of cheap costume jewelry.