A movie’s premise can be implausible and still work. The audience does not have to buy into whatever it is that the hero and heroine are after long as we believe that the movie’s characters believe in it. But in “Leap Year,” the premise and its ensuing complications are so preposterous that it just can’t work, despite the best efforts of its adorable leads and postcard-pretty settings. It has become something of a tradition to lead off the year with a weak romantic comedy, and we can cross the 2010 edition off the list.

The ones to blame here are screenwriters Deborah Kaplan and Harry Elfont, also responsible for the mind-numbingly painful Surviving Christmas and Made of Honor. Once, many years ago, they made a fresh and endearing little film about a high school graduation party with a cast of promising newcomers and a soundtrack of unexpected treats. That was “Can’t Hardly Wait.” But since then, they have made one formulaic, synthetic failure after another.

Their first movie had heart. Everything since then has been about what can get studio approval. These are “elevator pitch” movies — the premise is based on a successful film and can be summarized in an elevator ride, and the deal-makers rely on established stars with a lot of appeal to make it work. Their last movie tweaked “My Best Friend’s Wedding” by making the BFF who wanted to stop the nuptials the guy. This one takes the idea of the glossy “French Kiss,” the classics “I Know Where I’m Going” and “It Happened One Night” and about two dozen other squabbling-couple-dealing-with-a-disaster-prone-journey movies and, as Woody Allen once said of his mother’s cooking, “puts it through the de-flavorizing machine.”

Amy Adams in full twinkle mode plays Anna. She is, predictably, uptight, a bit of a control freak, and dying to have her perfect-on-paper boyfriend propose to her. But alas, he gives her diamond earrings instead of an engagement ring, just before he leaves for a meeting in Dublin. When her ne’er-do-well father (John Lithgow) — can his unreliability be the source of her need to be in control? — tells her that in Ireland, women can propose on February 29, she decides that in spite of her lifelong fear of flying, she will pop over to Dublin to pop the question.

But of course the best-laid plans of perky heroines in romantic comedies always go wrong, and here enters the complication. Handsome bartender Matthew Goode, for reasons that are too dull to go into, agrees to get her the rest of the way to Dublin, and all of the predictable problems line up like an obstacle course between us and time to go home. Car problems. Party crashing. Having to pretend to be married. Some flickers of romance that are quickly crushed by some un-funny contrivances and pratfalls. Sigh. Sigh. Sigh.