A dumb premise doesn’t necessarily doom a romantic adventure film. One need only think of the many Hitchcock pictures, from “The 39 Steps” to “Notorious” to “North by Northwest,” that have worked splendidly despite inherently silly plots. The key, of course, is that the central idea has to be clever enough to make you smile and forget its absurdity for the duration and at least make sense within its own contrived universe, and that it has to be worked out with charm and a degree of warmth. “Mr. & Mrs. Smith,” which just happens to share its title with one of Hitch’s pictures (albeit an uncharacteristic one from 1941), fails on all these counts; in fact, it misses by a country mile. It may just be the stupidest movie of the summer–which is saying quite a lot, given the fare we’ve had thus far. And Brad Pitt and Angelina Jolie, who play married hit-people for rival government agencies who try to rub one another out when they discover each other’s line of work and then are pursued jointly by their employers when they fail, prove singularly unlikable individually, and despite their rumored off-stage tryst they register little on-screen chemistry. Even worse, the movie degenerates quickly into nothing but a succession of loud, bruising chases and violent, noisy shootouts. This charmless, bombastically overproduced picture generates plenty of carnage but remarkably little excitement, romance or fun.

The picture opens cute, with John and Jane Smith meeting during a military round-up in Bogota following an assassination: though strangers, they pretend to be together to save themselves when the authorities are searching for a single gun-person. Five or six years later (they can’t seem quite to agree), they’re talking to a marriage counselor–i.e., straight into the camera–about their marriage; at home, a big, rambling place, they discuss redecorating rooms and enjoy big dinners she’s prepared while he’s off at work. But they’ve been concealing from one another their real lives as agency killers, he for a rather run-down outfit where he works beside high-strung loudmouth Eddie (Vince Vaughn) and she for an ultra-slick all-woman outfit where her closest associate is Jasmine (Kerry Washington). The plot kicks in when they’re both instructed to rub out Benjamin Danz (Adam Brody), a young guy who’s being transported across the desert in the custody of a government team. By some happenstance they set up their ambushes at the same spot in the wilderness and wind up blasting away at one another rather than the target, leading each to suspect that the other is out to dissolve the marriage in the most permanent possible way. There follow lots of battles in which they face off–the most notable being a drawn-out sequence in which they effectively destroy their house–but eventually they find themselves in league against a small army of common foes. To explain why would spoil whatever twists the script has up its sleeve, but it will come as little surprise that when shooting at one another the duo seem the worst marksmen in the world, but they’re both wonderfully accurate when firing their guns at others.

The intended punch-line to all the mayhem is that the couple’s marriage is reinvigorated by their joint experience, but that’s something the movie just asserts in its overly adorable fashion (more direct-to-the-audience quips at the end) rather than successfully demonstrating. Any message of that sort is, at any rate, entirely secondary to the meat of the picture–the all-too-numerous action sequences with guns blazing, stunt men leaping about, cars careening through freeway traffic and explosions going off. As “The Bourne Identity” proved, director Doug Liman is exceptionally good at staging such set-pieces, but here it’s all just empty display, with absolutely nothing at stake, and over the course of more than two hours it’s simply exhausting. Whatever genuine humor it has comes from Pitt’s smirking delivery of the script’s occasional sharp line (usually one with a rather juvenile double meaning), although overall the golden boy preens too much, continuing to exude the same overconfident smugness he did in “Ocean’s Twwlve,” and from Vaughn’s manic turn as an hysterical mother’s boy. (Jolie looks great, of course, but she doesn’t do much here she hasn’t already accomplished as Lara Croft.) The only other member of the cast who makes any impression at all is Brody (of “The OC”), who in his brief turn manages to be a likable geek reminiscent of the Anthony Michael Hall of the old John Hughes days. “Mr. & Mrs. Smith” is an elaborate production–with a budget of well over $100 million, if the reports are correct–and the money shows in the visuals: Jeff Mann’s production design and Bojan Bazelli’s cinematography are top-drawer. John Powell’s insistently overbusy score, however, is a serious distraction.

But all the banal banter and mindless action that’s preceded comes to seem almost palatable when “Mr. & Mrs. Smith” arrives at the big revelation of what lies behind everything that’s happened. Simply put, the explanation offered is completely idiotic; even the dullest viewer will realize immediately that it renders the entire plot not just pointless, but a hugely unnecessary waste of lives and resources, since the “problem” all the dark doings aim to solve could have easily been settled with the expenditure of a couple of bullets. Of course, for the script to have recognized that fact and accepted the consequences would have meant there would have been no movie–something that would have been a great benefit to all, filmmakers and audiences alike.