That sigh: you’d know it anywhere. Those puffed, baggy cheeks, the thin, pale lips stuck together like the crusts of a day-old sandwich; the whoosh of expelled breath calibrated to convey precisely the level of annoyance experienced by a self-important network president made to wait for an elevator … the sigh that can mean only one thing: Bill Murray’s back, and more aggravated than ever.

Sardonic wink, roll of eyes…

And in his new hit, “Groundhog Day,” which grossed more than $28 million in its first two weeks, Murray has a vehicle that allows him full range for his astonishing gift for exasperation. He plays a smugly repellent TV weatherman doomed to relive over and over the same miserable day, snowbound in Punxsutawney, Pa., for the idiotic Groundhog Day ceremonies. Murray shifts smoothly from simple impatience with his producer, Andie MacDowell, to the suicidal frenzy in which he drives off a cliff with an uncaged groundhog in his lap. Admittedly, the emotional verisimilitude of that scene was enhanced when the animal bit Murray three times during filming. (“A costar that bites you once, well, I can accept that,” Murray told an interviewer. “A costar that bites you twice, well, now, that’s a problem.”) But it shouldn’t matter; motivation is extraneous to Murray’s art, which consists of getting the maximum return from the minimum visible expenditure of energy.

“Bill projects to the casual observer, ‘I’m just goofing off here’,” says John McNaughton, who directed him in “Mad Dog and Glory,” opening this Friday. He rarely gives more than a half smile, never lifts both eyebrows when one is sufficient. Murray studied sneering from John Belushi himself (his mentor at Chicago’s Second City troupe and “Saturday Night Live”), but a Murray sneer is to a Belushi one as the Mona Lisa’s smile is to Joan Rivers’s. Acting a scene, Murray’s face registers a sequence of emotions as precisely as a galvanometer. Between expressions the needle always falls back to zero, which is what makes it possible to watch him for virtually every second of a 103-minute-long comedy about claustrophobia and tedium. With a hotter personality-Robin Williams, say–the movie would be unviewable.

Weary nod, shrug, nervous glance right at camera over costar’s shoulder…

Murray’s gift is especially evident in “Mad Dog and Glory,” a Richard Price fable noire in which he plays Frank Milo, a mob loan shark who befriends a Chicago policeman played by Robert De Niro. This was an irresistible opportunity for Murray to expand into dramatic parts, for the first time since the disastrous 1984 failure of “The Razor’s Edge.” Murray plays against type as a gangster, but, not to get too far from his roots, a gangster whose hobby is stand-up comedy. And he makes a convincing one. His performance “is about as close to the real Bill Murray as we’d want to get,” says coproducer Steve Jones, “. . . a Bill Murray who has a propensity to brood, who isn’t glib and funny and happy.”

Happy? Is there anyone who thinks Murray is happy? Glib, funny, yes-but could someone with his gift for projecting irritation be happy? Murray’s friends keep hinting at his Celtic strain, the black moods that descend on him like the fog on Lake Michigan. But this seems to presuppose a darker past than he actually possesses. As the fifth of nine children, growing up in a comfortable Chicago suburb, he may just be suffering from the world’s worst case of middle-child syndrome.

Putting Murray and De Niro on screen together was one of those seemingly can’t miss ideas that turn out somehow not quite right, like peanut butter on a bagel. Murray says the idea was “Bobby’s,” and if he was awed by “Bobby” he never showed it. “Bill is a guy who’ll walk up to the pope and pinch his nose,” says McNaughton. The problem is that De Niro is also cast against type, in the implausible role of a timid cop. One of the great Method actors, De Niro hurls himself into timidity with his accustomed ferocity. Shyness boils up inside him and breaks over his features in great waves; he packs every gesture with diffidence until he practically makes his ears droop. Meanwhile Murray, with his effortless mastery of technique, manages to project menace even through lines like, “I’m the expediter of your dreams, pal.” Right up until the climactic fistfight, Murray does the unthinkable-he dominates De Niro, showing a danger and explosive violence we’ve never seen before.

Devilish grin, boyish grin …

It is Murray’s genius to make acting look easy. Also, just by standing there he demonstrates that you don’t have to be especially handsome. “Bill represents a kind of shambling irony; he’s heroic and disreputable at the same time,” says his friend and fellow Ghostbuster Harold Ramis, who directed “Groundhog Day.” Yet by Hollywood standards he lives an exemplary home life in an upstate New York town with his wife of more than a decade, Mickey, and two school-age sons. His hobby is as wholesome as they come: he collects minor-league baseball teams.

Except for “The Razor’s Edge,” his career has followed a smooth upward trajectory from sketch comic to comedy superstar (“Ghostbusters,” 1984) to director (“Quick Change,” 1990) to quasi-romantic leading man. MacDowell puts off going to bed with him for practically the whole movie, but succumbs, because in character or out, “you can’t help but be charmed by Bill.” This is true even when he’s not trying. As a guest of ultraurbane talk-show host Charlie Rose last month, Murray’s demeanor was less like an actor plugging his new movie than a real-estate developer dragged before a community group to explain why he paved over the town’s historic cemetery. “Am I making any sense at all, Charlie?” he asked anxiously. In a failed good-will gesture to the citizens of Punxsutawney, allegedly miffed because “Groundhog Day” was actually filmed in Woodstock, Ill., he managed to misspell the name of their town. At last, when the evereffusive Rose invited him back in a few weeks to plug his next movie, Murray neglected to leap up, grab both of his host’s hands and announce, looking right at the camera, “I’ll be here!” Instead he …

Looks away, shrugs, sighs …