Tami Parris went shopping for a new SUV earlier this month, just as the tumult over the big, thirsty machines was reaching a peak.

Environmentalists had stepped up their rage against sport-utility vehicles for being heavy polluters, and evangelical Christians piled on with crusades suggesting SUVs were somehow immoral. Even the director of the National Highway Traffic Safety Administration weighed in with serious concerns about the vehicles' safety.

All the noise meant nothing to Parris, a 33-year-old Woodbridge woman expecting her first child. She bought an SUV anyway -- but like many car buyers these days, she still managed to add to the anxiety of U.S. auto executives: Parris rejected a giant Ford Expedition in favor of the more stylish, more carlike Nissan Murano.

Her choice is part of a pronounced shift in the car-buying habits of Americans, who are turning away from the long-popular truck-based SUVs built by U.S. automakers and embracing import SUVs that handle like cars.

The mighty sport-utility vehicles that symbolized the swagger of the 1990s just as surely as finned behemoths captured the confident 1950s are giving way to a more refined breed. American automakers earn almost all their profits on SUVs and other light trucks, which now account for more than half of their inventory, and they are scrambling to keep up with the changes in mood that foreign carmakers seem to have anticipated.

"The defection rate from the old sport-utility class started to climb about four years ago," said Art Spinella, head of CNW Marketing Research, an Oregon-based auto industry consulting firm. In 1998, he said, only 3 percent of people who owned truck-based SUVs -- such as Chevrolet Blazers or Ford Explorers -- traded them in on something different.

Last year that number climbed to 40 percent, with virtually all the defectors switching to smaller or car-based SUVs. There suddenly is a crop of import vehicles to meet that need, even as General Motors thunders into the marketplace with the gigantic Hummer. The Murano debuted this month, and Honda's Pilot already was shaking things up -- both are slick crossovers with the handling of a car but the higher ride and visibility of a sport-utility.

One of the auto industry's leading trend watchers, WardsAuto.com, calls the new breed "cross-utility vehicles," or CUVs. From zero reported sales in 1996, the midsize CUV segment has exploded. It nearly doubled from 2000 to 2001 and rose 39 percent in 2002 to sales of more than 812,000 vehicles, WardsAuto's numbers show.

That's almost as many as the 874,000 large SUVs sold last year, a number that declined from the previous year for the first time in a decade, according to WardsAuto. Overall SUV sales rose in 2002, but at a slower rate than that of crossover vehicles.

Add in the rising chorus of criticism from environmental and safety groups, as well as increasing oil prices and the prospect of war with Iraq, and suddenly a reliable icon of the modern age starts to look vulnerable.

"A lot of people are gunning for SUVs these days. It's putting more pressure on the industry, no doubt," said Ronald A. Tadross, senior auto analyst for Banc of America Securities in New York.

U.S. automakers play down the pressures even as they race to respond to them. "Americans continue their love affair with SUVs," said Gloria Bergquist of the Alliance of Automobile Manufacturers. "This is the ultimate American lifestyle question. Americans love their vehicles . . . and they don't like having anyone else telling them what they should be driving."

After all, big SUVs are marketed as more than vehicles; they're three tons of American dream, monsters of metal and technology that devour the landscape with not only speed but entitlement. Anyone can be Lewis or Clark in an Eddie Bauer Jeep Cherokee, and without the saddle sores.

But a diverse crowd of naysayers has been questioning that image. Last year, the Evangelical Environmental Network aired its "What would Jesus drive?" television ads, urging drivers to think about the environmental and safety impact of their choice of vehicle.

At the same time, the radical environmentalist group Earth Liberation Front vandalized SUVs in several East Coast locations, including Richmond and Georgetown. A Boston group called Earth on Empty has put fake traffic tickets on SUVs across the country and wound up in the Doonesbury comic strip. Last summer, National Public Radio's popular "Car Talk" hosts, Tom and Ray Magliozzi, got Stonyfield Farm to put an anti-SUV slogan on its yogurt lids.

Most recently, a California group led by conservative commentator Arianna Huffington has begun airing television ads suggesting that SUVs support terrorism by consuming a disproportionate amount of Middle Eastern oil products.

The SUV opponents felt they gained legitimacy two weeks ago when NHTSA chief Jeffrey W. Runge told an audience in Detroit that he was personally disturbed by the rollover risk of SUVs and their potential to demolish other vehicles in a crash. Runge vowed to make regulating SUV safety one of the top priorities of his agency.

"This is like a wake-up call -- even in a conservative, business-oriented administration this issue has not escaped the regulatory process," said Joan Claybrook, president of Public Citizen. "I think if U.S. manufacturers don't start to change right now, they're going to be caught short."

The truth is, not all SUVs are as safe and strong as their image suggests. Because most ride high, they are more prone to roll over than sedans. SUV occupants are three times as likely to die in a rollover crash as people in passenger cars, according to NHTSA. And rollovers are increasing as SUVs take over more of the car market.

High-end models equipped with anti-lock brakes, side-impact air bags and stability control get better safety ratings, as do the more carlike crossovers. NHTSA rates SUVs for their resistance to rollovers. Among the top-rated models are the 2003 Acura MDX four-door 4x4, with side air bags, while the lowest rating went to the 2003 Chevrolet Blazer 4x2. For a complete listing of the ratings, check the NHTSA Web site (www.nhtsa.dot.gov/NCAP/Cars/2003SUVs.html).

Because of their size, SUVs pose a threat to smaller vehicles. When someone driving an SUV or pickup truck collides with the front section of a passenger car, the car driver is six times as likely to die as the driver of the bigger vehicle, according to NHTSA.

SUVs and pickups are not required to meet the same gas-mileage and emissions standards as passenger cars, because they are classified as light trucks. Currently, new cars have to average 27.5 miles per gallon, while light trucks must average 20.7 miles per gallon. The Bush administration has proposed raising light trucks to 22.2 miles per gallon over the next three years.

So far, such statistics do not seem to be discouraging the car-buying public. Spinella said he surveyed more than 4,700 potential SUV buyers both before and after the TV ads equating fuel use with terrorism, and only a fraction of a percent -- 11 people -- said they gave the charges any credence. The responders also showed little fear of rollovers, while they felt strongly that buying an SUV would keep them safer if someone crashed into them at an intersection.

Drivers aren't even scared away by SUVs' higher sticker prices compared with cars. Manufacturers have sustained the craze through the nation's economic slowdown by offering incentives such as cheap financing and attractive leasing plans. There also are tax incentives for SUV ownership -- the government allows businesses to claim depreciation on them as light trucks.

In the end, though, no force is stronger than the chemistry that led Tami Parris of Woodbridge to pick the Murano over the Expedition. Just as women led the switch from station wagons to minivans in the 1980s, they're also pushing the shift from truck-based SUVs to the crossover types, Spinella said.

Parris said she wanted something that would let her ride up high and would keep her young family safe, but that there was no way she would consider a boring minivan. "That's not my style," she said. The Ford Expedition "was just too big," she said, but the Murano had a "terrific ride."

Detroit's designers really want to capture that kind of business. DaimlerChrysler will introduce a model called the Pacifica later this year, and next year Ford plans to unveil both a tall, spacious sedan (the Five Hundred) and a wagonlike crossover (the Freestyle) that are aimed at buyers such as Parris. Ford also announced plans to introduce this year a small gas-electric hybrid SUV that gets nearly 40 miles per gallon.

"We're seeing there's customer appeal for further options" within the world of SUVs, said Mike Moran, a spokesman for Ford. "We think it's an evolution in customer preference."

Some experts worry that the U.S. carmakers are giving imports too big a head start in getting such vehicles on the road. If the nation gets into a protracted war with Iraq, and if gas prices head up over $2 a gallon, the results could be devastating.

But the three major domestic carmakers are confident the momentum of the large-SUV phenomenon -- helped along by incentives -- will last long enough to tide them over.

"The Big Three will be trying to push those until they come out with some of their own bigger CUV products over the next three to four years," said Haig Stoddard, manager of industry analysis at WardsAuto.com. "In the long term . . . SUV growth will stop and they will see more of a shift toward those cross-utilities."

While GM worked to expand its Hummer line with the smaller-but-still-huge H2, right, Nissan came up with the Murano, a carlike SUV that is stealing buyers from the behemoths.