MIDDLE AGE CRAZY -- AMC Skyline, Loehmann's Plaza, New Carrollton, NTI Springfield, NTI White Flint, Roth's Silver Spring West, Roth's Tysons Corner, Showcase Beltway Plaza, Showcase Turnpike, Tenley Circle and Town Center Laurel.

Consider the sad case of a middle-aged Houston businessman. Despite his beautiful wife, fancy house and swimming pool, there's an empty feeling. His wife seems boring, his job demeaning, his whole life, in fact, a waste. So he trades his Oldsmobile for a Porsche, his three-piece suit for a pair of jeans and his wife for a Dallas Cowgirl -- and wonders why he's still unhappy.

Meet Bobby Lee Burnett, the only man in America who hasn't heard of Gail Sheehy.

At first "Middle Age Crazy" sounds like the same old trendy sob story we've been bombarded with in books and magazines over the last few "me"-oriented years. On the other hand, just because pop psychologists have analyzed the subject to death doesn't mean mid-life crises aren't painful, legitimate rites of passage. Thanks to sensitive performances by Bruce Dern and Ann Margaret, and a well-written script, this movie turns out to be anything but predictable. It's an affecting, bittersweet and frequently very funny portrait of a marriage in flux.

As Bobby Lee Burnett turns 40, he feels he's botched up his life. His job -- designing taco stands for a Houston franchise called Senor Abe's -- has lost its appeal, if indeed it ever had any. His troubled teenaged son, irascible father, blithering mother and assorted tacky neighbors all demand his attention. And his wife, Sue Ann, also approaching middle age, has suddenly taken the Marabel Morgan approach to sex. "She's probably at home right now figuring out how we can do it in the dryer," he complains wearily to a friend one morning.

Everything he sees reminds him of his wasted, misspent youth. He begins to indulge in elaborate, hilarious fantasies. "Every year you kids put on these silly hats," he tells his son's high-school class in a mordantly funny imaginary valedictory, "and some other kid in a silly hat tells you you're the future. Well you can't all be the future, there's not that much future to go around. You'll be lucky to catch on at the phone company. Look at your parents -- you don't want to be the future."

Enter an escape, in the form of the Dallas Cowgirl cheerleader (Deborah Wakeham).But after a whirlwind affair, Bobby Lee decides that irresponsibility isn't all it's cracked up to be.

Dern plays Bobby Lee with the perfect combination of love and despair, and Ann Margret is touching and believable as Sue Ann, who is equally troubled by her fading sexuality. Her eloquent performance should put her sex-kitten image to rest once and for all.

Despite a somewhat patronizing view of Texas life -- everybody has two first names (how cute), talks with a twang and spends up a storm -- the filmmakers never lose respect for the integrity of this mixed-up family. This compassion, obvious in every scene, saves the film from mediocrity.

Among the supporting players, Eric Christmas and Helen Hughes are especially effective as Bobby Lee's parents. Possibly the most endearing figure in his father, a crusty old guy with a refreshingly candid attitude toward aging. His birthday message to his son: "You think 40's bad? Try 64. 64's the s---s."

"Middle Age Crazy" is based on a country-and-western song by Jerry Lee Lewis and produced by puppet impresarios Sid and Marty Krofft with funding from the Canadian Film Development Corporation -- an unlikely background if there ever was one. That it all comes together so well makes this movie all the more worthwhile.