The sports-car market is colliding head-on with the no-frills 1990s.

Consumers who once gladly parted with big hunks of their paychecks to buy flashy two-door toys are growing up. Saddled with mortgage payments and tuition bills, they now favor more functional vehicles _ small and midsize four-door sedans, minivans, sport-utility vehicles, even pickup trucks. Chrysler Corp.'s Jeep division reports that many of its new customers are former sports-car owners.

``The last of the baby boomers have hit 30, and they've outgrown the small two-door sports car,'' says James Bragg, chief executive officer of Fighting Chance, an information service for new-car shoppers that is based in Long Beach, Calif. Meanwhile, ever steeper sports-car prices and sky-high insurance payments are turning away potential buyers in their late teens and 20s _ traditionally, the core market for sports cars.

The sports-car segment of the car market was once, strictly speaking, confined to sleek and speedy racers but now encompasses all kinds of coupes and small convertibles. The evidence that the segment is declining is everywhere. This week, Ford Motor Co. temporarily idled the factory that builds Mustangs. Sales of the sporty car are down nearly 18 percent for the first eight months of this year. Sales of the Ford Probe were off 37.3 percent through August, compared with last year, and the factory that makes it is cutting jobs. Other sporty cars with plummeting sales: the Chevrolet Corvette, Chevrolet Camaro, Alfa Romeo Spider, three Porsche models and the Toyota Celica.

Sports cars used to be as important for single men and women on the prowl as a date on Saturday night. But as sports-car owners settled down and started families, flashy cars with tiny back seats (or none at all) became impractical luxuries.

``It was fun driving, and I liked all the attention it got because of the color,'' says 23-year-old Nicole Noggle of the blazing-yellow Geo Storm that she bought in 1991 for $9,000 when she was still single. ``It was really a flirtatious car, and that's another reason I don't have it now,'' says Mrs. Noggle, who was married in 1993 and is expecting her first child this month. She now drives a Nissan Altima sedan, which she says is more suitable in its size for her occupation as a nanny. ``I didn't even have a trunk in the Geo because it was a hatchback,'' she says.

Mr. Bragg of Fighting Chance reflects on the cost factor: ``In the '90s, with everyone worrying about being downsized and putting money away for retirement, financial decisions are more about what's rational and practical,'' he says.

Alfred Bolden, a 40-year-old Detroit resident, fondly remembers both of his Ford Probes. In 1989, he was one of the first owners, cruising around in a blue $18,000 model; three years later, he bought the updated 1993 version. It was a fun, comfortable drive for Mr. Bolden, who is 5 feet 5 inches tall. But taller passengers complained that their heads brushed the roof, and their knees were jammed into their chests in the back seat. Seating three or more pals wasn't even an option.

Last year, Mr. Bolden broke down and bought a spacious Infiniti J30 luxury sedan from Nissan Motor Co. ``As I grew in income and age, my taste changed, and the Infiniti fit better,'' he says.

The sports-car market has always been fickle. Sales typically boom when a new model is launched, then rapidly fall off as the next great model is introduced. That's why the auto industry is not mourning the decline of this segment.

Bob Thomas, president of Nissan's U.S. arm, boasts about how his company has shed its sports-car image and is instead reaping much more profit and sales volume from its family of four-door Altima, Maxima and Sentra sedans, as well as its Pathfinder sport-utility vehicles and Quest minivans. ``I think the sports-car segment will decline to a level where it is populated by a few brand names,'' Mr. Thomas predicts.

Consider Nissan's Z-car line. Sales of the 280ZX sports car peaked in 1979 at 86,007, but its successor model, the 300ZX, sold only 3,552 in the just-ended 1995 model year. Nissan's lineup now includes the 300ZX and the 240SX sports cars, but that will change. ``Strategically in the future, we will only have one sports car,'' Mr. Thomas says.

Auto makers once used their newest sports cars to introduce the latest, greatest gadgets, designs and color schemes. Now, sedans and sport-utility vehicles are chock-full of gizmos and have sporty designs _ another reason sports-car fans are making the switch. ``We are noticing more of our customers trading in sports cars for our sedans,'' says Tom McDonald, a Mazda Motor Corp. spokesman. ``We can give you a 626 (midsize sedan) with leather, a V-6 engine, a five-speed shift and very similar _ if not the same _ suspension'' as in Mazda's MX6 sports car.

It wasn't just space but also safety that convinced 30-year-old Vaughn Currie of Detroit to ditch his sporty gold 1989 Honda Prelude and buy a green-and-beige Ford Explorer _ the popular, beefy, four-wheel-drive utility vehicle. Mr. Currie, who with his wife, Kim, has two young sons, used to dread every snowy, icy or rainy day, fearing for his family's safety. He worried that someone would hit them in the tiny Prelude. ``In the Explorer,'' he says, ``a lot of my burden has been lifted.''