It has finally happened.

In what is sure to be a psychological blow to Detroit, foreign-based auto brands have surpassed traditional domestic brands in U.S. retail sales, according to the latest vehicle registration data from R.L. Polk & Co.

Through May, 52.9 percent of the new vehicles registered by purchasers were import brands, up from 49.0 percent a year earlier. If the trend holds, this will be the first year that import brands generate the majority of U.S. retail sales.

Retail registrations of domestic brands totaled 2,554,636 through May, down 7.2 percent compared with the same period in 2005. Meanwhile, registrations of import brands rose 8.2 percent to 2,864,409 units.

The shift in retail share has been sharp - almost precipitous - and the downturn has hit Big 3 brands across the board. Lincoln and Hummer are the only domestic brands that enjoyed higher retail registrations through May.

Among import brands, the six biggest gainers were Toyota, Volkswagen, Land Rover, Porsche, Mercedes and Suzuki.

The Polk data does not include fleet registrations, which cover the sales of vehicles to corporate fleets and daily rental companies. If fleet sales are included, the Big 3 brands collectively generated 54.7 percent of total U.S. registrations through May.

Fleet sales tend to be less profitable and may mask how well an automaker is doing with average consumers. "We feel retail registrations are a good indicator of what the natural marketplace is demanding," said Lonnie Miller, Polk's director of industry analysis.

The ascendancy of the import brands has been building for many years, Miller said. "I'm not terribly surprised, given the trend," he said. "The imports were on (the Big 3's) heels and were getting closer and closer."

Trucks suffer

Much of the Big 3's decline can be traced to rising gasoline prices and declining demand for trucks.

U.S. pickup sales declined 9.9 percent in the first six months of the year. Minivan sales are down 8.3 percent and traditional SUV sales are down 12.3 percent.

In the truck segment, only crossovers are doing well. In the first six months, sales rose 2.4 percent.

The declining popularity of trucks has been bad news for the Big 3. "In the 1990s, this town was built on the SUV business," said Ford Motor Co.'s sales analyst George Pipas.

General Motors' one bright spot is Hummer, which defied slumping demand for SUVs. Hummer's retail registrations nearly tripled as the H3 enjoyed a successful debut. But GM's newest brand could not offset the weak performances of such older siblings as Buick, Saturn and GMC. Excluding Saab, GM's overall retail registrations fell 7.7 percent.

Ford got a boost from its Lincoln luxury brand after the successful debut of the Zephyr sedan, but it wasn't enough to offset Ford division's slumping sales of pickups and SUVs. Overall, retail registrations for Ford's domestic brands slid 5.7 percent.

Chrysler division's retail registrations fell sharply, while Dodge and Jeep suffered more modest downturns. Overall, the Chrysler group's registrations fell 8.0 percent.

This fall, the Chrysler group pins its hopes on a slew of new products that include three new Jeeps plus the Chrysler Aspen and Dodge Nitro SUVs, and the redesigned Chrysler Sebring car.

Think small

As truck sales stumble, demand for small and mid-sized cars are heating up, and the biggest beneficiaries are the imports.

Buoyed by strong sales of the Civic and Fit, Honda Motor Co. enjoyed a 9.3 percent increase in retail registrations. Riding strong sales of the Yaris subcompact and the Scion brand, Toyota's retail registrations rose 12.5 percent.

Among the Japanese Big 3, only Nissan stumbled. Its retail registrations declined 1.2 percent, although it will get help this fall when it introduces the Versa subcompact plus the redesigned Altima sedan.

The import brands' gains have been building for years, and few observers expect that trend to change in the near future.

But it may be too early to assume that the Big 3's retail market share will remain under 50 percent for the entire year. In theory, another summer price war could allow GM, Ford and the Chrysler group to win back some of their retail market share, Miller said.

Despite an aggressive promotion by Chrysler, both Ford and GM have vowed they won't be dragged into another summer blowout sale. But it's early, and Miller predicts the market-share split between the Big 3 and import brands could tighten.

"I still think it's going to be close," he said. "You've got a lot of aggressive tactics that are going to be employed. This data doesn't reflect any of those results yet."

Amy Wilson contributed to this report

The Polk data does not include fleet registrations, which cover the sales of vehicles to corporate fleets and daily rental companies. If fleet sales are included, the Big 3 brands collectively generated 54.7 percent of total U.S. registrations through May.

The Polk data does not include fleet registrations, which cover the sales of vehicles to corporate fleets and daily rental companies. If fleet sales are included, the Big 3 brands collectively generated 54.7 percent of total U.S. registrations through May.